MFS VARIABLE INSURANCE TRUST
497, 1996-09-27
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<PAGE>
 
<TABLE>
<S>                          <C>
MFS-REGISTERED TRADEMARK- EMERGING GROWTH SERIES-SM-
MFS-REGISTERED TRADEMARK- VALUE SERIES-SM-
MFS-REGISTERED TRADEMARK- RESEARCH SERIES-SM-
MFS-REGISTERED TRADEMARK- TOTAL RETURN SERIES-SM-
MFS-REGISTERED TRADEMARK- WORLD GOVERNMENTS SERIES-SM-
                             PROSPECTUS
                             May 1, 1996 As Revised
                             August 1, 1996
</TABLE>
 
- --------------------------------------------------------------------------------
 
<TABLE>
<S>                                       <C>
MFS-Registered Trademark- VARIABLE
INSURANCE TRUST-SM-
</TABLE>
 
MFS  Variable Insurance Trust (the "Trust") is an open-end management investment
company offering insurance company separate  accounts a selection of  investment
vehicles  for  variable  annuity  and  variable  life  insurance  contracts (the
"Contracts"). Currently the  Trust offers  shares of beneficial  interest of  12
separate  mutual fund series (individually  or collectively hereinafter referred
to as a "Series" or  the "Series"), five of which  are offered pursuant to  this
Prospectus:
 
- -- MFS  EMERGING GROWTH  SERIES (the "Emerging  Growth Series"),  which seeks to
   provide long-term growth of capital;
 
- -- MFS VALUE SERIES (the "Value Series"), which seeks capital appreciation;
 
- -- MFS RESEARCH SERIES (the "Research Series"), which seeks to provide long-term
   growth of capital and future income;
 
- -- MFS TOTAL RETURN SERIES (the "Total Return Series"), which seeks primarily to
   provide above-average income  (compared to a  portfolio invested entirely  in
   equity  securities)  consistent with  the prudent  employment of  capital and
   secondarily to provide  a reasonable  opportunity for growth  of capital  and
   income; and
 
- -- MFS  WORLD GOVERNMENTS SERIES  (the "World Governments  Series"), which seeks
   not only preservation, but  also growth, of  capital, together with  moderate
   current income;
                              -------------------
 
THE  EMERGING  GROWTH  SERIES, THE  VALUE  SERIES  AND THE  RESEARCH  SERIES ARE
INTENDED FOR  INVESTORS WHO  UNDERSTAND  AND ARE  WILLING  TO ACCEPT  THE  RISKS
ENTAILED  IN SEEKING  LONG-TERM GROWTH OF  CAPITAL. BECAUSE  OF THEIR INVESTMENT
POLICIES PERMITTING INVESTMENT IN FOREIGN SECURITIES, INVESTMENTS IN EACH SERIES
MAY BE SUBJECT TO A GREATER DEGREE OF RISK THAN INVESTMENTS IN OTHER  INVESTMENT
COMPANIES WHICH INVEST ENTIRELY IN DOMESTIC SECURITIES.
                              -------------------
<PAGE>
  THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
    EXCHANGE  COMMISSION  OR ANY  STATE SECURITIES  COMMISSION NOR  HAS THE
     SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION
       PASSED UPON  THE ACCURACY  OR ADEQUACY  OF THIS  PROSPECTUS.  ANY
             REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.
                              -------------------
 
INVESTMENTS IN THE MONEY MARKET SERIES ARE NEITHER INSURED NOR GUARANTEED BY THE
U.S.  GOVERNMENT  AND THERE  IS NO  ASSURANCE THAT  THE SERIES  WILL BE  ABLE TO
MAINTAIN A STABLE NET ASSET VALUE OF $1.00 PER SHARE.
                              -------------------
 
SHARES OF THE TRUST  ARE AVAILABLE AND  ARE BEING MARKETED  AS A POOLED  FUNDING
VEHICLE FOR LIFE INSURANCE COMPANIES WRITING ALL TYPES OF CONTRACTS.
 
This  Prospectus sets forth  concisely the information about  each Series that a
prospective investor should know  before applying for  the Contracts offered  by
the  separate accounts of certain  insurance companies ("Participating Insurance
Companies"). Investors are advised  to read this  Prospectus and the  applicable
Contract  prospectus  carefully and  retain them  for  future reference.  If you
require more detailed information, a  Statement of Additional Information  dated
May  1, 1996, as revised August 1, 1996, as amended or supplemented from time to
time ("SAI"), is available  upon request without charge  and may be obtained  by
calling  or by writing  to the Shareholder  Servicing Agent (see  back cover for
address and phone number). The SAI, which is incorporated by reference into this
Prospectus, has  been filed  with the  Securities and  Exchange Commission  (the
"SEC").
 
   INVESTORS SHOULD READ THIS PROSPECTUS AND RETAIN IT FOR FUTURE REFERENCE.
<PAGE>
TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                                                                       PAGE
                                                                                                       ---
  <S>                                                                                                  <C>
  1.  Expense Summary................................................................................   4
  2.  Investment Concept of the Trust................................................................   5
  3.  Condensed Financial Information................................................................   6
  4.  Investment Objectives and Policies.............................................................  10
      MFS Emerging Growth Series.....................................................................  10
      MFS Value Series...............................................................................  10
      MFS Research Series............................................................................  11
      MFS Total Return Series........................................................................  11
      MFS World Governments Series...................................................................  12
  5.  Investment Techniques..........................................................................  13
  6.  Additional Risk Factors........................................................................  20
  7.  Management of the Series.......................................................................  23
  8.  Information Concerning Shares of Each Series...................................................  26
      Purchases and Redemptions......................................................................  26
      Net Asset Value................................................................................  26
      Distributions..................................................................................  26
      Tax Status.....................................................................................  27
      Description of Shares, Voting Rights and Liabilities...........................................  27
      Performance Information........................................................................  27
      Expenses.......................................................................................  28
      Shareholder Communications.....................................................................  29
  Appendix A -- Description of Bond Ratings..........................................................  A-1
</TABLE>
 
                                       3
<PAGE>
1.  EXPENSE SUMMARY
 
ANNUAL OPERATING EXPENSES (AS A PERCENTAGE OF AVERAGE NET ASSETS):
<TABLE>
<CAPTION>
                                                                MFS
                                                              EMERGING     MFS        MFS
                                                               GROWTH     VALUE     RESEARCH
                                                               SERIES     SERIES     SERIES
                                                              --------   --------   --------
<S>                                                           <C>        <C>        <C>
Management Fee..............................................  0.75%      0.75%      0.75%
Other Expenses (after fee reduction)(3).....................  0.25%(1)   0.25%(1)   0.25%(1)
                                                               ---       --------    ---
Total Operating Expenses (after fee reduction)..............  1.00%(1)   1.00%(1)   1.00%(1)
 
<CAPTION>
 
                                                                MFS        MFS
                                                               TOTAL      WORLD
                                                               RETURN    GOVERNMENTS
                                                               SERIES     SERIES
                                                              --------   --------
<S>                                                           <C>        <C>        <C>
Management Fee..............................................  0.75%      0.75%
Other Expenses (after fee reduction)(3).....................  0.25%(1)   0.25%(2)
                                                               ---       --------
Total Operating Expenses (after fee reduction)..............  1.00%(1)   1.00%(2)
<FN>
- ------------------------
(1)        The  Adviser has agreed to  bear, subject to reimbursement,  expenses for each of  the Emerging Growth Series, Value
           Series, Research Series  and Total  Return Series  such that  each Series'  aggregate operating  expenses shall  not
           exceed,  on an annualized basis, 1.00% of  the average daily net assets of  the Series from November 2, 1994 through
           December 31, 1996, 1.25% of  the average daily net assets  of the Series from January  1, 1997 through December  31,
           1998,  and 1.50%  of the average  daily net assets  of the  Series from January  1, 1999 through  December 31, 2004;
           provided however, that this obligation may be terminated or revised at any time. See "Information Concerning  Shares
           of  Each Series--Expenses" below. Absent  this expense arrangement, "Other  Expenses" and "Total Operating Expenses"
           would be 1.00% and 1.75% for  the Value Series. Absent this expense  arrangement, "Other Expenses" for the  Emerging
           Growth  Series, Research Series and Total Return Series, would  be 2.16%, 3.15%, and 2.02%, respectively, and "Total
           Operating Expenses" would be 2.91%, 3.90%, and 2.77%, respectively, for these Series.
(2)        The Adviser has agreed to bear, subject to reimbursement, until December 31, 2004, expenses of the World Governments
           Series such that  the Series'  aggregate operating expenses  do not  exceed 1.00%, on  an annualized  basis, of  its
           average  daily net assets. See  "Information Concerning Shares of Each  Series--Expenses" below. Absent this expense
           arrangement, "Other Expenses" and "Total Operating Expenses" would be 1.24% and 1.99%, respectively.
(3)        Each Series has an expense offset arrangement which reduces the Series' custodian fee based upon the amount of  cash
           maintained  by  the  Series with  its  custodian  and dividend  disbursing  agent,  and may  enter  into  other such
           arrangements and  directed  brokerage arrangements  (which  would  also have  the  effect of  reducing  the  Series'
           expenses). Any such fee reductions are not reflected under "Other Expenses."
</TABLE>
 
    The   purpose  of  the  expense  table  above  is  to  assist  investors  in
understanding the various costs  and expenses that a  shareholder of the  Series
will  bear directly or indirectly. The  Series' annual operating expenses do not
reflect  expenses  imposed  by  separate  accounts  of  Participating  Insurance
Companies  through which  an investment  in a  Series is  made or  their related
Contracts. A separate account's expenses are disclosed in the prospectus through
which the Contract relating to that separate account is offered for sale.
 
                                       4
<PAGE>
2.  INVESTMENT CONCEPT OF THE TRUST
 
    The Trust is an open-end, registered management investment company comprised
of the following twelve series:  Emerging Growth Series, Value Series,  Research
Series,  Growth With Income Series, Total  Return Series, Utilities Series, High
Income Series, World  Governments Series,  Strategic Fixed  Income Series,  Bond
Series,  Limited  Maturity Series  and  Money Market  Series.  Each Series  is a
segregated, separately  managed  portfolio of  securities.  All of  the  Series,
except the Utilities Series, World Governments Series and Strategic Fixed Income
Series, are diversified. Additional series may be created from time to time. The
Trust  was organized as a  business trust under the  laws of The Commonwealth of
Massachusetts by a Declaration of Trust dated February 1, 1994.
 
    The Trust  currently  offers shares  of  each Series  to  insurance  company
separate  accounts that fund Contracts. Separate accounts may purchase or redeem
shares at  net asset  value without  any sales  or redemption  charge. Fees  and
charges imposed by a separate account, however, will affect the actual return to
the   holder  of  a  Contract.  A  separate  account  may  also  impose  certain
restrictions or limitations on the  allocation of purchase payments or  Contract
value  to one or more Series, and not  all Series may be available in connection
with a particular Contract. Prospective investors should consult the  applicable
Contract  prospectus for information regarding fees and expenses of the Contract
and separate account and any  applicable restrictions or limitations. The  Trust
assumes no responsibility for such prospectuses.
 
    Shares  of the Series are offered  to the separate accounts of Participating
Insurance Companies  that are  affiliated  or unaffiliated  ("shared  funding").
Shares  of the Series may serve as  the underlying investments for both variable
annuity  and  variable  life  insurance  contracts  ("mixed  funding").  Due  to
differences  in tax treatment or other  considerations, the interests of various
Contract owners might at some time be in conflict. The Trust currently does  not
foresee  any such conflict. Nevertheless, the Trust's Trustees intend to monitor
events in  order to  identify any  material irreconcilable  conflicts which  may
possibly arise and to determine what action, if any, should be taken in response
thereto.  If such a conflict were to occur, one or more separate accounts of the
Participating Insurance Companies might be required to withdraw its  investments
in  one  or  more  Series. This  might  force  a Series  to  sell  securities at
disadvantageous prices.
 
    Individual Contract holders are not the "shareholders" of the Trust. Rather,
the Participating  Insurance  Companies  and their  separate  accounts  are  the
shareholders  or  investors, although  such  companies may  pass  through voting
rights to their Contract holders.
 
    The Trust's Board of Trustees provides broad supervision over the affairs of
the Trust and the Series.  Massachusetts Financial Services Company, a  Delaware
corporation  ("MFS" or the "Adviser"), is the investment adviser to each Series.
A majority of the Trustees of the Trust are not affiliated with the Adviser. The
Adviser is responsible for the management of  the assets of each Series and  the
officers  of the Trust  are responsible for the  operations. The Adviser manages
the Series'  portfolios  from day  to  day  in accordance  with  the  investment
objectives and policies of each Series. The selection of investments and the way
they  are managed  depend on the  conditions and  trends in the  economy and the
financial marketplaces.
 
                                       5
<PAGE>
3.  CONDENSED FINANCIAL INFORMATION
 
The following financial information (presented  for each Series which  commenced
investment  operations prior  to December 31,  1995) has been  audited since the
commencement of  investment operations  of such  Series and  should be  read  in
conjunction with the financial statements included in the Series' Annual Reports
to  shareholders. These financial statements  are incorporated by reference into
the SAI in reliance  upon the report of  the Series' independent auditors  given
upon  their authority as experts in accounting and auditing. The Series' current
independent auditors  are  Deloitte &  Touche  LLP.  The Value  Series  had  not
commenced investment operations prior to December 31, 1995.
 
                             EMERGING GROWTH SERIES
 
<TABLE>
<CAPTION>
                                                                      PERIOD ENDED
                                                                   DECEMBER 31, 1995*
                                                                   ------------------
<S>                                                                <C>
Per share data (for a share outstanding throughout the period):
Net asset value--beginning of period.............................        $10.00
                                                                         ------
Income from investment operations#--
  Net investment incomeSection...................................        $ 0.01
  Net realized and unrealized gain on investments................          1.74
                                                                         ------
    Total from investment operations.............................        $ 1.75
                                                                         ------
Less distributions declared to shareholders--
  From net investment income.....................................        $(0.01)
  From net realized gain on investments..........................         (0.31)
  Tax return of capital..........................................         (0.02)
                                                                         ------
    Total distributions declared to shareholders.................        $(0.34)
                                                                         ------
Net asset value--end of period...................................        $11.41
                                                                         ------
                                                                         ------
Total return.....................................................         17.41%++
Ratios (to average net assets)/Supplemental dataSection:
  Expenses.......................................................          1.00%+
  Net investment income..........................................          0.10%+
Portfolio turnover...............................................            73%
Net assets at end of period (000 omitted)........................        $3,869
<FN>
- ------------------------
        *  For the period from the commencement of investment operations, July 24, 1995 to December 31, 1995.
        +  Annualized.
       ++  Not annualized.
        #  Per share data is based on average shares outstanding.
  Section  The  Adviser voluntarily agreed to maintain the expenses of the  Series at not more than 1.00% of average daily net
           assets. To the extent actual expenses were over these limitations, the net investment loss per share and the ratios
           would have been:
 
Net investment loss..............................................       $(0.18)
Ratios (to average net assets):
  Expenses.......................................................         2.91       %+
  Net investment loss............................................        (1.78)%+
</TABLE>
 
                                       6
<PAGE>
                                RESEARCH SERIES
 
<TABLE>
<CAPTION>
                                                                      PERIOD ENDED
                                                                   DECEMBER 31, 1995*
                                                                   ------------------
<S>                                                                <C>
Per share data (for a share outstanding throughout the period):
Net asset value--beginning of period.............................        $10.00
                                                                         ------
Income from investment operations#--
  Net investment incomeSection...................................        $ 0.05
  Net realized and unrealized gain on investments and foreign
    currency transactions........................................          1.01
                                                                         ------
    Total from investment operations.............................        $ 1.06
                                                                         ------
Less distributions declared to shareholders--
  From net investment income.....................................        $(0.03)
  From net realized gain on investments and foreign currency
    transactions.................................................         (0.14)
                                                                         ------
    Total distributions declared to shareholders.................        $(0.17)
                                                                         ------
Net asset value--end of period...................................        $10.89
                                                                         ------
                                                                         ------
Total return.....................................................         10.62%++
Ratios (to average net assets)/Supplemental dataSection:
  Expenses.......................................................          1.00%+
  Net investment income..........................................          1.15%+
Portfolio turnover...............................................            28%
Net assets at end of period (000 omitted)........................        $2,530
<FN>
- ------------------------
        *  For the period from the commencement of investment operations, July 26, 1995 to December 31, 1995.
        +  Annualized.
       ++  Not annualized.
        #  Per share data is based on average shares outstanding.
  Section  The Adviser voluntarily agreed to maintain the expenses of the  Series at not more than 1.00% of average daily  net
           assets. To the extent actual expenses were over these limitations, the net investment loss per share and the ratios
           would have been:
 
Net investment loss..............................................       $(0.08)
Ratios (to average net assets):
  Expenses.......................................................         3.90       %+
  Net investment loss............................................        (1.73)%+
</TABLE>
 
                                       7
<PAGE>
                              TOTAL RETURN SERIES
 
<TABLE>
<CAPTION>
                                                                      PERIOD ENDED
                                                                   DECEMBER 31, 1995*
                                                                   ------------------
<S>                                                                <C>
Per share data (for a share outstanding throughout the period):
Net asset value--beginning of period.............................        $10.00
                                                                         ------
Income from investment operations#--
  Net investment incomeSection...................................        $ 0.41
  Net realized and unrealized gain on investments and foreign
    currency transactions........................................          2.32
                                                                         ------
    Total from investment operations.............................        $ 2.73
                                                                         ------
Less distributions declared to shareholders--
  From net investment income.....................................        $(0.25)
  From net realized gain on investments and foreign currency
    transactions.................................................         (0.23)
                                                                         ------
    Total distributions declared to shareholders.................        $(0.48)
                                                                         ------
Net asset value--end of period...................................        $12.25
                                                                         ------
                                                                         ------
Total return.....................................................         27.34%++
Ratios (to average net assets)/Supplemental dataSection:
  Expenses.......................................................          1.00%+
  Net investment income..........................................          3.83%+
Portfolio turnover...............................................            16%
Net assets at end of period (000 omitted)........................        $2,797
<FN>
- ------------------------
        *  For the period from the commencement of investment operations, January 3, 1995 to December 31, 1995.
        +  Annualized.
       ++  Not annualized.
        #  Per share data is based on average shares outstanding.
  Section  The  Adviser voluntarily agreed to maintain the expenses of the  Series at not more than 1.00% of average daily net
           assets. To the extent  actual expenses were  over these limitations, the  net investment income  per share and  the
           ratios would have been:
 
Net investment income............................................        $0.22
Ratios (to average net assets):
  Expenses.......................................................         2.77%+
  Net investment income..........................................         2.09%+
</TABLE>
 
                                       8
<PAGE>
                            WORLD GOVERNMENTS SERIES
 
<TABLE>
<CAPTION>
                                                                       YEAR ENDED          PERIOD ENDED
                                                                   DECEMBER 31, 1995    DECEMBER 31, 1994*
                                                                   ------------------   ------------------
<S>                                                                <C>                  <C>
Per share data (for a share outstanding throughout each period):
Net asset value--beginning of period.............................        $ 9.82               $10.00
                                                                         ------               ------
Income from investment operations#--
  Net investment incomeSection...................................        $ 0.63               $ 0.17
  Net realized and unrealized gain (loss) on investments and
    foreign currency transactions................................          0.78                (0.09)
                                                                         ------               ------
    Total from investment operations.............................        $ 1.41               $ 0.08
                                                                         ------               ------
Less distributions declared to shareholders--
  From net investment income.....................................        $(0.42)              $(0.17)
  In excess of net investment income.............................         (0.54)               (0.09)
  Tax return of capital..........................................         (0.10)                  --
                                                                         ------               ------
    Total distributions declared to shareholders.................        $(1.06)              $(0.26)
                                                                         ------               ------
Net asset value--end of period...................................        $10.17               $ 9.82
                                                                         ------               ------
                                                                         ------               ------
Total return.....................................................         14.38%                0.79%++
Ratios (to average net assets)/Supplemental dataSection:
  Expenses##.....................................................          1.00%                1.00%+
  Net investment income..........................................          6.05%                4.68%+
Portfolio turnover...............................................           211%                  62%
Net assets at end of period (000 omitted)........................        $7,424               $2,881
</TABLE>
 
- ------------------------
 
<TABLE>
<C>        <S>
        *  For the period from the commencement of investment operations, June 14, 1994 to December 31, 1994.
        +  Annualized.
       ++  Not annualized.
        #  Per share data is based on average shares outstanding.
       ##  For fiscal years after September 1, 1995, the Series' expenses are calculated without reduction for fees paid
           indirectly.
  Section  The  Adviser voluntarily agreed to maintain the expenses of the Series at not more than 1.00% of average daily net
           assets. To the extent actual  expenses were over these  limitations, the net investment  income per share and  the
           ratios would have been:
</TABLE>
 
<TABLE>
<S>                                                                <C>      <C>
Net investment income............................................  $0.53    $0.16
Ratios (to average net assets):
  Expenses.......................................................   1.99%    1.10%+
  Net investment income..........................................   5.09%    4.58%+
</TABLE>
 
                                       9
<PAGE>
4.  INVESTMENT OBJECTIVES AND POLICIES
 
    Each  Series has  different investment  objectives which  it pursues through
separate investment policies, as described below. The differences in  objectives
and policies among the Series can be expected to affect the degree of market and
financial  risk to which each  Series is subject and  the return of each Series.
The investment  objectives and  policies of  each Series  may, unless  otherwise
specifically  stated, be changed by the Trustees  of the Trust without a vote of
the shareholders. Any investment  involves risk and there  is no assurance  that
the objectives of any Series will be achieved.
 
    In  addition  to the  specific  investment practices  described  below, each
Series may also engage in certain  investment techniques as described under  the
caption  "Investment  Techniques"  below  and  in  the  SAI  under  the  caption
"Investment Techniques." The Series' investments  are subject to certain  risks,
as described in the above-referenced sections of this Prospectus and the SAI and
as described below under the caption "Additional Risk Factors."
 
MFS  EMERGING GROWTH SERIES --  The Series seeks to  provide long-term growth of
capital. Dividend  and interest  income from  portfolio securities,  if any,  is
incidental to the Series' investment objective of long-term growth of capital.
 
    The  Series' policy is to invest primarily (I.E., at least 80% of its assets
under normal circumstances) in common stocks of companies that MFS believes  are
early  in  their  life  cycle  but which  have  the  potential  to  become major
enterprises (emerging  growth  companies).  Such companies  generally  would  be
expected to show earnings growth over time that is well above the growth rate of
the  overall economy  and the  rate of inflation,  and would  have the products,
technologies, management and  market and other  opportunities which are  usually
necessary  to become more widely recognized as growth companies. Emerging growth
companies can  be of  any size,  and the  Series may  invest in  larger or  more
established  companies whose rates of earnings growth are expected to accelerate
because of  special  factors,  such as  rejuvenated  management,  new  products,
changes  in consumer demand, or basic changes in the economic environment. While
the Series will invest primarily in common stocks, the Series may, to a  limited
extent,  seek  appreciation in  other types  of  securities such  as convertible
securities  and  warrants  when  relative  values  make  such  purchases  appear
attractive  either as  individual issues  or as  types of  securities in certain
economic environments.
 
    The nature of investing in  emerging growth companies involves greater  risk
than  is customarily associated with  investments in more established companies.
Emerging growth companies often have limited product lines, markets or financial
resources, and  they may  be dependent  on one-person  management. In  addition,
there  may be less research  available on many promising  small and medium sized
emerging growth companies, making  it more difficult to  find and analyze  these
companies.  The  securities  of  emerging  growth  companies  may  have  limited
marketability and may be subject to more abrupt or erratic market movements than
securities of larger, more established  growth companies or the market  averages
in  general. Shares of the Series, therefore, are subject to greater fluctuation
in value than shares  of a conservative  equity fund or of  a growth fund  which
invests entirely in proven growth stocks.
 
    Consistent  with its investment objective  and policies described above, the
Series may also invest up to 25% (and generally expects to invest not more  than
15%)  of  its  net  assets  in  foreign  securities  (including  emerging market
securities and Brady Bonds) which are not traded on a U.S. exchange.
 
MFS VALUE SERIES --  The Value Series' investment  objective is to seek  capital
appreciation.  Dividend income,  if any,  is a  consideration incidental  to the
Series' objective of capital appreciation.
 
    While the Series'  policy is to  invest primarily in  common stocks, it  may
seek  appreciation in other types of  securities such as fixed income securities
(which may  be unrated),  convertible bonds,  convertible preferred  stocks  and
warrants  when relative values  make such purchases  appear attractive either as
individual issues or as  types of securities  in certain economic  environments.
The  Series may invest  in fixed income securities  rated lower than "investment
grade" (rated Ba or lower by  Moody's Investors Service, Inc. ("Moody's") or  BB
or  lower  by Standard  &  Poor's Ratings  Services  ("S&P") or  Fitch Investors
Service, Inc.  ("Fitch")) (commonly  known  as "junk  bonds") or  in  comparable
unrated securities, when, in the
 
                                       10
<PAGE>
opinion  of the Adviser,  such an investment presents  a greater opportunity for
appreciation with  comparable  risk  to  an  investment  in  "investment  grade"
securities. Under normal market conditions, the Series will invest not more than
25%  of its net assets in these  securities. For a description of these ratings,
see Appendix A to this Prospectus.
 
    Consistent with its investment objective  and policies described above,  the
Series  may also invest up to 50% (and generally expects to invest not more than
25%) of  its  net  assets  in  foreign  securities  (including  emerging  market
securities and Brady Bonds) which are not traded on a U.S. exchange. There is no
formula  as to the percentage of assets that  may be invested in any one type of
security. Cash, commercial paper, short-term obligations, repurchase  agreements
or  debt securities are held to provide  for future purchases of common stock or
other securities and may also be held as a temporary defensive measure when  the
Adviser determines security markets to be overvalued.
 
MFS  RESEARCH SERIES -- The Research  Series' investment objective is to provide
long-term growth of capital and future income.
 
    The portfolio  securities  of  the  Research  Series  are  selected  by  the
investment  research analysts in  the Equity Research Group  of the Adviser. The
Series' assets are allocated to  industry groups (E.G., pharmaceuticals,  retail
and  computer software). The  allocation by industry group  is determined by the
analysts acting together. Individual analysts are then responsible for selecting
what they view  as the  securities best suited  to meet  the Series'  investment
objective within their assigned industry group.
 
    The  Research Series'  policy is to  invest a substantial  proportion of its
assets in the  common stocks  or securities  convertible into  common stocks  of
companies  believed  to  possess  better than  average  prospects  for long-term
growth. A smaller proportion of the assets may be invested in bonds,  short-term
obligations, preferred stocks or common stocks whose principal characteristic is
income   production  rather  than   growth.  Such  securities   may  also  offer
opportunities for growth  of capital  as well  as income.  In the  case of  both
growth  stocks  and  income  issues,  emphasis is  placed  on  the  selection of
progressive,  well-managed   companies.   The   Series'   non-convertible   debt
investments,  if any, may consist of "investment grade" securities (rated Baa or
better by Moody's or BBB or better by S&P or by Fitch), and, with respect to  no
more  than  10%  of  the  Series' net  assets,  securities  in  the  lower rated
categories (rated Ba or lower by Moody's or  BB or lower by S&P or by Fitch)  or
securities  which the Adviser believes  to be of similar  quality to these lower
rated securities (commonly  known as "junk  bonds"). For a  description of  bond
ratings, see Appendix A to this Prospectus.
 
    Consistent  with its investment objective  and policies described above, the
Series may  also invest  up  to 20%  of its  net  assets in  foreign  securities
(including emerging market securities) which are not traded on a U.S. exchange.
 
MFS TOTAL RETURN SERIES -- The Total Return Series' primary investment objective
is to provide above-average income (compared to a portfolio invested entirely in
equity  securities) consistent with  the prudent employment  of capital, and its
secondary objective is to provide a reasonable opportunity for growth of capital
and income, since many securities offering a better than average yield may  also
possess  growth potential. Thus, in selecting  securities for its portfolio, the
Series considers each of  these objectives. Under  normal market conditions,  at
least  25% of the Total  Return Series' assets will  be invested in fixed income
securities, and at least 40% and no more than 75% of the Series' assets will  be
invested in equity securities.
 
    The  Series' policy is  to invest in  a broad list  of securities, including
short-term obligations. The list  may be diversified not  only by companies  and
industries,  but also  by type of  security. Fixed income  securities and equity
securities (which  include:  common and  preferred  stocks; securities  such  as
bonds,  warrants  or  rights that  are  convertible into  stock;  and depositary
receipts for those  securities) may  be held by  the Series.  Some fixed  income
securities  may  also have  a  call on  common stock  by  means of  a conversion
privilege or attached warrants. The Total Return Series may vary the  percentage
of  assets invested in any one type of security in accordance with the Adviser's
interpretation of  economic and  money market  conditions, fiscal  and  monetary
policy  and underlying security values. The Series' debt investments may consist
of both "investment grade"
 
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<PAGE>
securities (rated Baa or better by Moody's or BBB or better by S&P or by  Fitch)
and  securities that are unrated or are in the lower rating categories (rated Ba
or lower by Moody's or BB or lower by S&P or by Fitch) (commonly known as  "junk
bonds")  including  up  to 20%  of  its  assets in  nonconvertible  fixed income
securities that  are in  these lower  rating categories  and comparable  unrated
securities (see "Additional Risk Factors" below). Generally, most of the Series'
long-term  debt investments will  consist of "investment  grade" securities. See
Appendix A to this Prospectus for a description of these ratings.
 
    The  Series  may  also  invest  in  United  States  government   securities,
including:  (1) U.S. Treasury  obligations, which differ  only in their interest
rates, maturities and times of issuance: U.S. Treasury bills (maturities of  one
year  or less); U.S. Treasury  notes (maturities of one  to ten years); and U.S.
Treasury bonds (generally maturities  of greater than ten  years), all of  which
are  backed  by  the full  faith  and credit  of  the U.S.  Government;  and (2)
obligations issued or  guaranteed by  U.S. Government  agencies, authorities  or
instrumentalities,  some of which are backed by the full faith and credit of the
U.S. Treasury, E.G., direct pass-through certificates of the Government National
Mortgage Association ("GNMA"); some of which  are supported by the right of  the
issuer  to borrow  from the U.S.  Government, E.G., obligations  of Federal Home
Loan Banks;  and some  of which  are backed  only by  the credit  of the  issuer
itself,   E.G.,   obligations  of   the   Student  Loan   Marketing  Association
(collectively,  "U.S.  Government  Securities").   The  term  "U.S.   Government
Securities"  also includes  interests in  trusts or  other entities representing
interests in obligations that  are backed by  the full faith  and credit of  the
U.S.  Government  or  are  issued  or guaranteed  by  the  U.S.  Government, its
agencies, authorities or instrumentalities.
 
    Consistent with its investment objective  and policies described above,  the
Series  may  also invest  up  to 20%  of its  net  assets in  foreign securities
(including emerging market securities and Brady Bonds) which are not traded on a
U.S. exchange.
 
MFS WORLD  GOVERNMENTS  SERIES  --  The  World  Governments  Series'  investment
objective is to seek not only preservation, but also growth of capital, together
with moderate current income.
 
    The  World  Governments Series  seeks  to achieve  its  investment objective
through  a   professionally  managed,   internationally  diversified   portfolio
consisting   primarily  of  debt  securities  and  to  a  lesser  extent  equity
securities. The  Series attempts  to provide  investors with  an opportunity  to
enhance  the  value  and increase  the  protection of  their  investment against
inflation and otherwise by taking  advantage of investment opportunities in  the
U.S. as well as in other countries where opportunities may be more rewarding. It
is  believed that diversification of assets  on an international basis decreases
the degree to which events  in any one country,  including the U.S., can  affect
the  entire portfolio. Although the percentage of the Series' assets invested in
securities issued  abroad  and  denominated  in  foreign  currencies  will  vary
depending on the state of the economies of the principal countries of the world,
their  financial markets  and the relationship  of their currencies  to the U.S.
dollar,  under  normal  conditions  the  Series'  portfolio  is  internationally
diversified.  However,  for  temporary  defensive  reasons  or  during  times of
international political or economic uncertainty or  turmoil, most or all of  the
Series' investments may be in the U.S.
 
    Under  normal economic  and market conditions,  at least 80%  of the Series'
portfolio is invested in  debt securities, such  as bonds, debentures,  mortgage
securities,  notes,  commercial paper,  obligations  issued or  guaranteed  by a
government or any of its political subdivisions, agencies or  instrumentalities,
certificates  of deposit, as well  as debt obligations which  may have a call on
common stock by means of a conversion privilege or attached warrants.
 
    Consistent with its investment objective  and policies described above,  the
Series may invest up to 100% (and generally expects to invest not more than 80%)
of  its net assets  in foreign securities  (including emerging market securities
and Brady  Bonds)  which  are  not  traded on  a  U.S.  exchange.  Although  the
percentage  of the Series'  assets invested in foreign  securities will vary, at
least 65% of the  Series' assets will  be invested in  at least three  different
countries,  one of which may be the  U.S., except when the Adviser believes that
investing for  temporary defensive  purposes is  appropriate. The  Adviser  will
determine  the amount of the World Governments  Series' assets to be invested in
the U.S. and the amount to be invested abroad. The U.S. assets will be  invested
in  high  quality  debt securities  and  the  remainder of  the  assets  will be
diversified among countries where opportunities for total return are expected to
be most attractive.  It is  currently expected that  investments within  foreign
 
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<PAGE>
countries  will be primarily in government  securities to minimize credit risks.
The Series  will not  invest 25%  or more  of the  value of  its assets  in  the
securities of any one foreign government. The portfolio will be managed actively
and the asset allocations modified as the Adviser deems necessary.
 
    The World Governments Series will purchase non-dollar securities denominated
in  the currency of countries where the interest rate environment as well as the
general economic climate provide an opportunity for declining interest rates and
currency appreciation.  If interest  rates decline,  such non-dollar  securities
will  appreciate in value. If the  currency also appreciates against the dollar,
the total investment in  such non-dollar securities  would be enhanced  further.
Conversely, a rise in interest rates or decline in currency exchange rates would
adversely  affect  the  Series' return.  Investments  in  non-dollar denominated
securities are  evaluated primarily  on the  strength of  a particular  currency
against the dollar and on the interest rate climate of that country. Currency is
judged  on the basis of fundamental  economic criteria (E.G., relative inflation
levels and  trends,  growth rate  forecasts,  balance of  payments  status,  and
economic  policies) as well as technical and  political data. In addition to the
foregoing, interest  rates  are  evaluated  on the  basis  of  differentials  or
anomalies  that  may  exist between  different  countries. The  Series  may hold
foreign currency received in connection  with investments in foreign  securities
and  in  anticipation of  purchasing foreign  securities. (See  "Additional Risk
Factors" below.)
 
    The phrase "preservation of capital"  when applied to a domestic  investment
company  is generally understood to imply that the portfolio is invested in very
low risk securities and that the major risk is loss of purchasing power  through
the  effects of inflation or major changes in interest rates. However, while the
World Governments  Series  invests in  securities  which are  believed  to  have
minimal credit risk, an error of judgment in selecting a currency or an interest
rate environment could result in a loss of capital.
 
    It  is  contemplated  that  the  World  Governments  Series'  long-term debt
investments will  consist primarily  of  securities which  are believed  by  the
Adviser  to be of relatively high quality.  If after the Series purchases such a
security, the quality of the  security deteriorates significantly, the  security
will be sold only if the Adviser believes it is advantageous to do so.
 
5.  INVESTMENT TECHNIQUES
 
    LENDING OF PORTFOLIO SECURITIES: Each of the Series may seek to increase its
income  by  lending portfolio  securities. Such  loans will  usually be  made to
member firms (and  subsidiaries thereof)  of the  New York  Stock Exchange  (the
"Exchange")  and to  member banks  of the Federal  Reserve System,  and would be
required to  be  secured  continuously  by collateral  in  cash,  U.S.  Treasury
securities  or an irrevocable letter of credit  maintained on a current basis at
an amount at least equal  to the market value of  the securities loaned. If  the
Adviser  determines to make securities  loans, it is intended  that the value of
the securities loaned would not exceed 10% of the value of the net assets of the
Series making the loans.
 
    EMERGING MARKET  SECURITIES: Consistent  with their  respective  objectives,
each  Series may invest in securities  of issuers whose principal activities are
located in  emerging market  countries. Emerging  market countries  include  any
country  determined by  the Adviser to  have an emerging  market economy, taking
into account a number of  factors, including whether the  country has a low-  to
middle-  income economy according  to the International  Bank for Reconstruction
and Development, the country's foreign  currency debt rating, its political  and
economic stability and the development of its financial and capital markets. The
Adviser  determines whether an  issuer's principal activities  are located in an
emerging  market  country  by  considering  such  factors  as  its  country   of
organization,  the principal trading market for its securities and the source of
its revenues and assets. The issuer's principal activities generally are  deemed
to  be  located  in a  particular  country if:  (a)  the security  is  issued or
guaranteed by the government of that country or any of its agencies, authorities
or instrumentalities;  (b)  the issuer  is  organized  under the  laws  of,  and
maintains  a principal office in that country;  (c) the issuer has its principal
securities trading market in that country; (d) the issuer derives 50% or more of
its total revenues from goods sold or services performed in that country; or (e)
the issuer has 50% or more of its assets in that country.
 
                                       13
<PAGE>
    BRADY  BONDS: Each of the Series (except  the Research Series) may invest in
Brady Bonds,  which are  securities  created through  the exchange  of  existing
commercial bank loans to public and private entities in certain emerging markets
for  new bonds in connection with debt restructurings under a debt restructuring
plan introduced by former U.S. Secretary of the Treasury, Nicholas F. Brady (the
"Brady Plan"). Brady Plan debt restructurings  have been implemented to date  in
Argentina,  Brazil, Bulgaria,  Costa Rica, Dominican  Republic, Ecuador, Jordan,
Mexico, Nigeria, Panama, the Philippines,  Poland, Uruguay and Venezuela.  Brady
Bonds  have been issued  only recently, and for  that reason do  not have a long
payment history.  Brady Bonds  may be  collateralized or  uncollateralized,  are
issued  in various currencies  (but primarily the U.S.  dollar) and are actively
traded  in   over-the-counter   secondary  markets.   U.S.   dollar-denominated,
collateralized  Brady  Bonds, which  may  be fixed-rate  bonds  or floating-rate
bonds, are generally  collateralized in full  as to principal  by U.S.  Treasury
zero  coupon bonds having the same maturity  as the bonds. Brady Bonds are often
viewed  as  having  three  or  four  valuation  components:  the  collateralized
repayment  of principal at final maturity; the collateralized interest payments;
the uncollateralized interest  payments; and any  uncollateralized repayment  of
principal at maturity (these uncollateralized amounts constituting the "residual
risk"). In light of the residual risk of Brady Bonds and the history of defaults
of countries issuing Brady Bonds with respect to commercial bank loans by public
and private entities, investments in Brady Bonds may be viewed as speculative.
 
    REPURCHASE  AGREEMENTS:  Each  of  the  Series  may  enter  into  repurchase
agreements in order to earn income on available cash or as a temporary defensive
measure. Under a repurchase agreement,  a Series acquires securities subject  to
the  seller's agreement  to repurchase  at a  specified time  and price.  If the
seller becomes subject to a proceeding  under the bankruptcy laws or its  assets
are  otherwise  subject to  a stay  order,  the Series'  right to  liquidate the
securities may be  restricted (during  which time  the value  of the  securities
could  decline).  As  discussed in  the  SAI,  each Series  has  adopted certain
procedures intended to minimize risk.
 
    "WHEN-ISSUED" SECURITIES: Each of the Series (except the Research Series and
the World Governments Series) may purchase securities on a "when-issued" or on a
"forward delivery" basis, which means that  the securities will be delivered  to
the  Series  at a  future  date usually  beyond  customary settlement  time. The
commitment to purchase a  security for which  payment will be  made on a  future
date  may be deemed a  separate security. In general, a  Series does not pay for
such securities  until received,  and does  not start  earning interest  on  the
securities  until the  contractual settlement  date. While  awaiting delivery of
securities purchased on such bases, a Series will normally invest in cash,  cash
equivalents and high grade debt securities.
 
    MORTGAGE "DOLLAR ROLL" TRANSACTIONS: Each of the Total Return Series and the
World Governments Series may enter into mortgage "dollar roll" transactions with
selected  banks and  broker-dealers pursuant to  which a  Series sells mortgage-
backed securities for  delivery in  the future  (generally within  30 days)  and
simultaneously  contracts to repurchase substantially similar (same type, coupon
and maturity) securities on  a specified future date.  A Series will only  enter
into covered rolls. A "covered roll" is a specific type of dollar roll for which
there  is an  offsetting cash  position or  a cash  equivalent security position
which matures  on or  before the  forward  settlement date  of the  dollar  roll
transaction.  In the  event that  the party  with whom  the Series  contracts to
replace substantially similar securities on a future date fails to deliver  such
securities,  the Series may not  be able to obtain  such securities at the price
specified in such contract and thus may not benefit from the price  differential
between the current sales price and the repurchase price.
 
    RESTRICTED  SECURITIES: Each of the Series  may purchase securities that are
not registered under the  Securities Act of 1933  (the "1933 Act")  ("restricted
securities"),  including  those  that  can be  offered  and  sold  to "qualified
institutional  buyers"  under  Rule  144A   under  the  1933  Act  ("Rule   144A
securities").  The Trust's Board of Trustees determines, based upon a continuing
review of the trading  markets for a specific  Rule 144A security, whether  such
security  is liquid and thus not subject  to the Series' limitation on investing
not more  than 15%  of its  net assets  in illiquid  investments. The  Board  of
Trustees  has  adopted guidelines  and delegated  to MFS  the daily  function of
determining and monitoring  the liquidity  of Rule 144A  securities. The  Board,
however,  will retain sufficient oversight and be ultimately responsible for the
determinations. The Board  will carefully  monitor each  Series' investments  in
Rule  144A  securities, focusing  on such  important  factors, among  others, as
 
                                       14
<PAGE>
valuation, liquidity and availability  of information. This investment  practice
could  have the effect of  decreasing the level of liquidity  in a Series to the
extent that qualified  institutional buyers  become for a  time uninterested  in
purchasing Rule 144A securities held in the Series' portfolio.
 
    CORPORATE  ASSET-BACKED SECURITIES: Each  of the Emerging  Growth Series and
the Total Return Series may  invest in corporate asset-backed securities.  These
securities,  issued by trusts and special  purpose corporations, are backed by a
pool  of  assets,  such  as   credit  card  and  automobile  loan   receivables,
representing the obligations of a number of different parties.
 
    Corporate  asset-backed securities  present certain risks.  For instance, in
the case of credit card receivables,  these securities may not have the  benefit
of  any security interest in the related collateral. Credit card receivables are
generally unsecured and the debtors are  entitled to the protection of a  number
of  state and federal consumer credit laws,  many of which give such debtors the
right to set off certain amounts owed on the credit cards, thereby reducing  the
balance  due. Most  issuers of  automobile receivables  permit the  servicers to
retain possession of the  underlying obligations. If the  servicer were to  sell
these  obligations to another  party, there is  a risk that  the purchaser would
acquire an interest superior  to that of the  holders of the related  automobile
receivables.  In addition, because of the large number of vehicles involved in a
typical issuance and technical  requirements under state  laws, the trustee  for
the  holders  of  the automobile  receivables  may  not have  a  proper security
interest in all of the obligations backing such receivables. Therefore, there is
the possibility  that recoveries  on  repossessed collateral  may not,  in  some
cases,  be available  to support  payments on  these securities.  The underlying
assets  (E.G.,  loans)  are  also  subject  to  prepayments  which  shorten  the
securities' weighted average life and may lower their return.
 
    Corporate  asset-backed  securities are  often backed  by  a pool  of assets
representing the obligations  of a number  of different parties.  To lessen  the
effect  of  failures by  obligors  on underlying  assets  to make  payments, the
securities  may  contain  elements  of  credit  support  which  fall  into   two
categories:  (i)  liquidity  protection;  and  (ii)  protection  against  losses
resulting from  ultimate  default  by  an  obligor  on  the  underlying  assets.
Liquidity  protection  refers to  the provision  of  advances, generally  by the
entity administering the pool of assets, to ensure that the receipt of  payments
on  the underlying  pool occurs in  a timely fashion.  Protection against losses
resulting from ultimate  default ensures payment  through insurance policies  or
letters of credit obtained by the issuer or sponsor from third parties. A Series
will  not pay any additional or separate  fees for credit support. The degree of
credit support  provided  for  each  issue  is  generally  based  on  historical
information  respecting the level of credit  risk associated with the underlying
assets. Delinquency or  loss in  excess of that  anticipated or  failure of  the
credit  support could  adversely affect  the return on  an investment  in such a
security.
 
    ZERO COUPON BONDS, DEFERRED INTEREST BONDS  AND PIK BONDS: The Value  Series
and  the Total Return Series  may invest in zero  coupon bonds. The Value Series
and the the Total Return Series may  also invest in deferred interest bonds  and
PIK  bonds. Zero coupon  and deferred interest bonds  are debt obligations which
are issued or purchased at a significant discount from face value. The  discount
approximates  the total  amount of interest  the bonds will  accrue and compound
over the period until maturity or the  first interest payment date at a rate  of
interest  reflecting the market  rate of the  security at the  time of issuance.
While zero  coupon  bonds do  not  require  the periodic  payment  of  interest,
deferred interest bonds provide for a period of delay before the regular payment
of interest begins. PIK bonds are debt obligations which provide that the issuer
thereof may, at its option, pay interest on such bonds in cash or in the form of
additional  debt obligations. Such investments  benefit the issuer by mitigating
its need for cash to meet debt service, but also require a higher rate of return
to attract  investors  who are  willing  to defer  receipt  of such  cash.  Such
investments  may experience greater volatility in market value due to changes in
interest rates than debt  obligations which make  regular payments of  interest.
Each  Series  will accrue  income  on such  investments  for tax  and accounting
purposes, as required, which is distributable to shareholders and which, because
no cash is received at the time of accrual, may require the liquidation of other
portfolio securities to satisfy the Series' distribution obligations.
 
                                       15
<PAGE>
    COLLATERALIZED  MORTGAGE OBLIGATIONS AND MULTICLASS PASS-THROUGH SECURITIES:
The  World  Governments  Series   may  invest  a  portion   of  its  assets   in
collateralized  mortgage  obligations  or  "CMOs,"  which  are  debt obligations
collateralized by mortgage loans or mortgage pass-through securities. Typically,
CMOs are collateralized  by certificates  issued by GNMA,  the Federal  National
Mortgage  Association  ("FNMA") or  the Federal  Home Loan  Mortgage Corporation
("FHLMC"), but also  may be collateralized  by whole loans  or private  mortgage
pass-through  securities (such collateral collectively  referred to as "Mortgage
Assets"). Each  of these  Series may  also invest  a portion  of its  assets  in
multiclass  pass-through securities which  are interests in  a trust composed of
Mortgage Assets. CMOs (which include multiclass pass-through securities) may  be
issued  by agencies, authorities or instrumentalities  of the U.S. Government or
by private originators of,  or investors in,  mortgage loans, including  savings
and  loan associations, mortgage  banks, commercial banks,  investment banks and
special purpose  subsidiaries of  the foregoing.  Payments of  principal of  and
interest  on the Mortgage  Assets, and any  reinvestment income thereon, provide
the funds to pay debt service on the CMOs or make scheduled distributions on the
multiclass pass-through securities. In a CMO, a series of bonds or  certificates
are  usually issued in multiple classes with different maturities. Each class of
CMOs, often  referred to  as  a "tranche,"  is issued  at  a specific  fixed  or
floating  coupon  rate and  has a  stated maturity  or final  distribution date.
Principal prepayments on the  Mortgage Assets may cause  the CMOs to be  retired
substantially  earlier than their stated maturities or final distribution dates,
resulting in a loss of all or part of the premium if any has been paid.  Certain
classes  of  CMOs have  priority  over others  with  respect to  the  receipt of
prepayments on the mortgages. Therefore, depending on the type of CMOs in  which
a  Series invests, the investment may be subject  to a greater or lesser risk of
prepayments than other types of mortgage-related securities.
 
    The World  Governments Series  may  also invest  in  parallel pay  CMOs  and
Planned  Amortization Class CMOs ("PAC Bonds"). Parallel pay CMOs are structured
to provide payments of principal  on each payment date  to more than one  class.
PAC  Bonds generally require payments of a specified amount of principal on each
payment date. PAC Bonds are always parallel pay CMOs with the required principal
payment on such securities having the  highest priority after interest has  been
paid  to all classes. For  a further description of  CMOs, parallel pay CMOs and
PAC Bonds and the risks related to transactions therein, see the SAI.
 
    STRIPPED MORTGAGE-BACKED SECURITIES: The World Governments Series may invest
a portion of its assets  in stripped mortgage-backed securities ("SMBS"),  which
are  derivative  multiclass  mortgage  securities  usually  structured  with two
classes  that   receive  different   proportions  of   interest  and   principal
distributions  from  an  underlying  pool  of  mortgage  assets.  For  a further
description of SMBS and the risks related to transactions therein, see the SAI.
 
    LOAN PARTICIPATIONS  AND OTHER  DIRECT INDEBTEDNESS:  Each of  the  Emerging
Growth Series, the Value Series and the Total Return Series may invest a portion
of  its  assets  in  "loan participations"  and  other  direct  indebtedness. By
purchasing a loan participation, a Series  acquires some or all of the  interest
of  a bank or other lending institution in  a loan to a corporate borrower. Many
such loans are secured, and most impose restrictive covenants which must be  met
by  the borrower.  These loans  are made  generally to  finance internal growth,
mergers, acquisitions, stock repurchases, leveraged buy-outs and other corporate
activities. Such loans may be in default  at the time of purchase. A Series  may
also  purchase other direct  indebtedness such as trade  or other claims against
companies, which generally represent money owed by the company to a supplier  of
goods  and  services. These  claims may  also be  purchased at  a time  when the
company is  in default.  Certain of  the loan  participations and  other  direct
indebtedness  acquired by  a Series may  involve revolving  credit facilities or
other standby financing commitments  which obligate a  Series to pay  additional
cash on a certain date or on demand.
 
    The highly leveraged nature of many such loans and other direct indebtedness
may  make such  loans especially  vulnerable to  adverse changes  in economic or
market conditions. Loan participations and other direct indebtedness may not  be
in  the form of  securities or may  be subject to  restrictions on transfer, and
only limited opportunities may exist to resell such instruments. As a result,  a
Series  may be unable to sell such investments  at an opportune time or may have
to resell them at less than fair market value. For a further discussion of  loan
participations,  other direct indebtedness and the risks related to transactions
therein, see the SAI.
 
                                       16
<PAGE>
    MORTGAGE PASS-THROUGH  SECURITIES: The  Total Return  Series and  the  World
Governments  Series  may invest  in  mortgage pass-through  securities. Mortgage
pass-through securities  are securities  representing  interests in  "pools"  of
mortgage  loans. Monthly  payments of interest  and principal  by the individual
borrowers on mortgages are passed through to the holders of the securities  (net
of  fees paid to the issuer or guarantor  of the securities) as the mortgages in
the underlying mortgage pools are paid off. Payment of principal and interest on
some  mortgage  pass-through  securities  (but  not  the  market  value  of  the
securities  themselves) may be  guaranteed by the  full faith and  credit of the
U.S. Government (in the case of securities guaranteed by GNMA); or guaranteed by
U.S. Government-sponsored  corporations  (such  as  FNMA  or  FHLMC,  which  are
supported only by the discretionary authority of the U.S. Government to purchase
the  agency's obligations). Mortgage pass-through  securities may also be issued
by  non-governmental  issuers  (such  as  commercial  banks,  savings  and  loan
institutions,  private mortgage insurance companies,  mortgage bankers and other
secondary market  issuers).  See the  SAI  for  a further  discussion  of  these
securities.
 
    INDEXED  SECURITIES: Each of  the Value Series, the  Total Return Series and
the World Governments  Series may invest  in indexed securities  whose value  is
linked  to  foreign currencies,  interest rates,  commodities, indices  or other
financial indicators. Most  indexed securities  are short  to intermediate  term
fixed  income securities whose values at maturity (I.E., principal value) and/or
interest rates rise or  fall according to  the change in  one or more  specified
underlying  instruments.  Indexed  securities may  be  positively  or negatively
indexed (I.E., their principal value or interest rates may increase or  decrease
if  the underlying instrument appreciates),  and may have return characteristics
similar to direct  investments in the  underlying instrument or  to one or  more
options  on the underlying  instrument. Indexed securities  may be more volatile
than the underlying instrument itself.
 
    SWAPS AND  RELATED TRANSACTIONS:  As one  way of  managing its  exposure  to
different  types of  investments, the  World Governments  Series may  enter into
interest  rate  swaps,  currency  swaps  and  other  types  of  available   swap
agreements,  such as caps, collars and floors. Swaps involve the exchange by the
Series with another party  of cash payments based  upon different interest  rate
indexes,  currencies, and other prices  or rates, such as  the value of mortgage
prepayment rates. For  example, in the  typical interest rate  swap, the  Series
might  exchange a sequence of  cash payments based on  a floating rate index for
cash payments based on  a fixed rate.  Payments made by both  parties to a  swap
transaction are based on a principal amount determined by the parties.
 
    The  World Governments  Series may also  purchase and sell  caps, floors and
collars. In a typical cap or floor agreement, one party agrees to make  payments
only  under specified circumstances, usually  in return for payment  of a fee by
the counterparty. For example, the purchase of an interest rate cap entitles the
buyer, to the  extent that a  specified index exceeds  a predetermined  interest
rate,  to receive payments of interest on a contractually-based principal amount
from the counterparty selling  such interest rate cap.  The sale of an  interest
rate  floor obligates the seller to make payments to the extent that a specified
interest rate falls below  an agreed-upon level.  A collar arrangement  combines
elements of buying a cap and selling a floor.
 
    Swap  agreements will tend to shift the Series' investment exposure from one
type of investment  to another. For  example, if the  Series agreed to  exchange
payments  in dollars for payments  in foreign currency, in  each case based on a
fixed rate, the swap  agreement would tend to  decrease the Series' exposure  to
U.S.  interest rates and increase its  exposure to foreign currency and interest
rates. Caps and  floors have  an effect similar  to buying  or writing  options.
Depending  on how they  are used, swap  agreements may increase  or decrease the
overall volatility of the Series' investments and its share price and yield.
 
    Swap agreements are sophisticated hedging instruments that typically involve
a small investment  of cash relative  to the  magnitude of risks  assumed. As  a
result,  swaps can be  highly volatile and  may have a  considerable impact on a
Series'
 
                                       17
<PAGE>
performance. Swap agreements are subject to risks related to the  counterparty's
ability   to  perform,   and  may  decline   in  value   if  the  counterparty's
creditworthiness deteriorates. A Series may also  suffer losses if it is  unable
to  terminate  outstanding  swap  agreements  or  reduce  its  exposure  through
offsetting transactions.
 
    Swaps, caps,  floors and  collars are  highly specialized  activities  which
involve  certain risks. See  the SAI for  further information on,  and the risks
involved in, these activities.
 
    OPTIONS ON SECURITIES: Each of the  Series (except the Research Series)  may
write  (sell) covered put and call options  and purchase put and call options on
securities. Each  of these  Series  will write  options  on securities  for  the
purpose  of increasing its return and/or to  protect the value of its portfolio.
In particular, where a  Series writes an option  that expires unexercised or  is
closed  out by the Series at  a profit, it will retain  the premium paid for the
option which will increase its gross income and will offset in part the  reduced
value  of the portfolio security underlying the option, or the increased cost of
portfolio securities to be acquired. In  contrast, however, if the price of  the
underlying  security moves adversely to the  Series' position, the option may be
exercised and the  Series will be  required to purchase  or sell the  underlying
security  at a disadvantageous price, which may  only be partially offset by the
amount of the premium. The  Series may also write  combinations of put and  call
options  on  the  same security,  known  as "straddles."  Such  transactions can
generate additional premium income but also present increased risk.
 
    By writing a call option on a  security, a Series limits its opportunity  to
profit  from any increase in the market  value of the underlying security, since
the holder will usually exercise  the call option when  the market value of  the
underlying  security exceeds the exercise price of the call. However, the Series
retains the risk of depreciation in value of securities on which it has  written
call options.
 
    Each  of these Series (except the Research  Series) may also purchase put or
call options in anticipation of  market fluctuations which may adversely  affect
the  value of its portfolio  or the prices of securities  that a Series wants to
purchase at a  later date. In  the event that  the expected market  fluctuations
occur,  the Series  may be able  to offset  the resulting adverse  effect on its
portfolio, in whole or in part, through the options purchased. The premium  paid
for  a put or call option plus any transaction costs will reduce the benefit, if
any, realized by  the Series upon  exercise or liquidation  of the option,  and,
unless the price of the underlying security changes sufficiently, the option may
expire without value to the Series.
 
    In  certain instances, the Emerging Growth  Series may enter into options on
Treasury securities that  are "reset"  options or  "adjustable strike"  options.
These  options provide for periodic adjustment of  the strike price and may also
provide for  the periodic  adjustment of  the  premium during  the term  of  the
option. The SAI contains a further discussion of these investments.
 
    OPTIONS  ON STOCK  INDICES: Each  of the  Emerging Growth  Series, the Value
Series and the Total Return Series may write (sell) covered call and put options
and purchase call and  put options on  stock indices. Each  of these Series  may
write  options on stock indices  for the purpose of  increasing its gross income
and to protect its portfolio against declines in the value of securities it owns
or increases in the value of securities to be acquired. When a Series writes  an
option  on a  stock index,  and the value  of the  index moves  adversely to the
holder's position, the option will not be exercised, and the Series will  either
close  out the option  at a profit or  allow it to  expire unexercised. A Series
will thereby retain the amount of  the premium, less related transaction  costs,
which  will increase its  gross income and  offset part of  the reduced value of
portfolio securities or the  increased cost of securities  to be acquired.  Such
transactions, however, will constitute only partial hedges against adverse price
fluctuations,  since any such fluctuations will be  offset only to the extent of
the premium received by  a Series for  the writing of  the option, less  related
transaction  costs.  In addition,  if  the value  of  an underlying  index moves
adversely to a  Series' option position,  the option may  be exercised, and  the
Series  will experience a loss which may  only be partially offset by the amount
of the premium received.
 
                                       18
<PAGE>
    Each of these Series may also purchase put or call options on stock  indices
in  order, respectively, to hedge its investments  against a decline in value or
to attempt to reduce the risk of missing a market or industry segment advance. A
Series' possible loss in either case will be limited to the premium paid for the
option, plus related transaction costs.
 
    "YIELD CURVE" OPTIONS: Each of the Value Series, the Total Return Series and
the World Governments Series  may enter into options  on the yield "spread,"  or
yield  differential,  between two  securities, a  transaction  referred to  as a
"yield curve" option, for hedging and non-hedging (an effort to increase current
income) purposes. In contrast to other types of options, a yield curve option is
based on the difference between the yields of designated securities rather  than
the  actual prices  of the  individual securities,  and is  settled through cash
payments. Accordingly, a yield curve option is profitable to the holder if  this
differential  widens (in the case of a call)  or narrows (in the case of a put),
regardless of  whether  the yields  of  the underlying  securities  increase  or
decrease.  Yield curve options written by a  Series will be covered as described
in the SAI.  The trading  of yield  curve options is  subject to  all the  risks
associated  with  trading  other  types of  options,  as  discussed  below under
"Additional Risk Factors"  and in  the SAI.  In addition,  such options  present
risks  of loss  even if the  yield on  one of the  underlying securities remains
constant, if the  spread moves  in a  direction or to  an extent  which was  not
anticipated.
 
    FUTURES  CONTRACTS AND OPTIONS ON FUTURES CONTRACTS: The Total Return Series
and the World  Governments Series  may purchase  and sell  futures contracts  on
foreign  or  domestic fixed  income securities  or  indices of  such securities,
including municipal bond indices  and any other indices  of foreign or  domestic
fixed  income  securities  that  may  become  available  for  trading  ("Futures
Contracts"). Each of these  Series may also purchase  and write options on  such
Futures  Contracts ("Options on Futures Contracts"). Each of the Emerging Growth
Series, the  Value Series  and the  Total Return  Series may  purchase and  sell
Futures  Contracts on stock indices, while the Emerging Growth Series, the Value
Series, the Total Return  Series and the World  Governments Series may  purchase
and  sell  Futures  Contracts  on  foreign  currencies  or  indices  of  foreign
currencies. Each of  these Series may  also purchase and  write Options on  such
Futures Contracts.
 
    Such  transactions  will  be  entered  into  for  hedging  purposes  or  for
non-hedging purposes to the extent permitted by applicable law. Each Series will
incur brokerage fees when it purchases and sells Futures Contracts, and will  be
required  to  maintain margin  deposits. In  addition, Futures  Contracts entail
risks. Although the Adviser believes that  use of such Contracts will benefit  a
Series, if its investment judgment about the general direction of exchange rates
or  the stock market is incorrect, the Series' overall performance may be poorer
than if it had not entered into any  such contract and the Series may realize  a
loss.  A  Series  will  not  enter  into  any  Futures  Contract  if immediately
thereafter the value  of securities  and other obligations  underlying all  such
Futures Contracts held by such Series would exceed 50% of the value of its total
assets.
 
    Purchases of Options on Futures Contracts may present less risk in hedging a
Series'  portfolio than the purchase or sale of the underlying Futures Contracts
since the potential loss is  limited to the amount  of the premium plus  related
transaction  costs,  although it  may  be necessary  to  exercise the  option to
realize any profit, which  results in the establishment  of a futures  position.
The writing of Options on Futures Contracts, however, does not present less risk
than  the trading of Futures Contracts and will constitute only a partial hedge,
up to  the  amount  of the  premium  received.  In addition,  if  an  option  is
exercised, a Series may suffer a loss on the transaction.
 
    Futures  Contracts and Options on Futures Contracts that are entered into by
a Series will be traded on U.S. and foreign exchanges.
 
    FORWARD CONTRACTS:  Each  of  the  Series may  enter  into  forward  foreign
currency  exchange contracts for the  purchase or sale of  a fixed quantity of a
foreign currency at a  future date ("Forward Contracts").  Each of these  Series
may  enter  into  Forward Contracts  for  hedging purposes  and  for non-hedging
purposes (I.E., speculative purposes). By entering into transactions in  Forward
Contracts  for hedging purposes, a Series may be required to forego the benefits
of advantageous changes in exchange rates and, in the case of Forward  Contracts
entered  into for non-hedging  purposes, a Series may  sustain losses which will
reduce its  gross  income. Such  transactions,  therefore, could  be  considered
speculative.  Forward Contracts are traded over-the-counter and not on organized
commodities or securities exchanges. As a result, Forward
 
                                       19
<PAGE>
Contracts operate in  a manner  distinct from  exchange-traded instruments,  and
their  use involves certain  risks beyond those  associated with transactions in
Futures Contracts or options traded on exchanges. A Series may choose to, or  be
required  to,  receive delivery  of  the foreign  currencies  underlying Forward
Contracts it has entered  into. Under certain circumstances,  such as where  the
Adviser  believes that the  applicable exchange rate is  unfavorable at the time
the currencies are received  or the Adviser anticipates,  for any other  reason,
that  the exchange rate will improve, the Series may hold such currencies for an
indefinite period of time. A  Series may also enter  into a Forward Contract  on
one  currency to  hedge against  risk of loss  arising from  fluctuations in the
value of a second currency (referred to as a "cross hedge") if, in the  judgment
of  the  Adviser, a  reasonable degree  of correlation  can be  expected between
movements in  the  values  of the  two  currencies.  Each of  these  Series  has
established  procedures  consistent with  statements of  the  SEC and  its staff
regarding the use of Forward Contracts by registered investment companies, which
requires use of segregated assets or "cover" in connection with the purchase and
sale of such contracts.
 
    OPTIONS ON FOREIGN CURRENCIES: Each of the Emerging Growth Series, the Value
Series, the Total Return  Series and the World  Governments Series may  purchase
and  write options on  foreign currencies ("Options  on Foreign Currencies") for
the purpose of  protecting against  declines in  the dollar  value of  portfolio
securities  and  against  increases  in  the dollar  cost  of  securities  to be
acquired. As in the case of other  types of options, however, the writing of  an
Option  on Foreign  Currency will  constitute only  a partial  hedge, up  to the
amount of the premium received, and a Series may be required to purchase or sell
foreign currencies at disadvantageous exchange rates, thereby incurring  losses.
The  purchase of an Option on Foreign Currency may constitute an effective hedge
against fluctuations in exchange rates although, in the event of rate  movements
adverse  to a Series' position, it may  forfeit the entire amount of the premium
paid for the option plus related transaction costs. A Series may also choose to,
or be required to, receive delivery of the foreign currencies underlying Options
on Foreign Currencies it has entered into. Under certain circumstances, such  as
where  the Adviser believes that the  applicable exchange rate is unfavorable at
the time the currencies are received  or the Adviser anticipates, for any  other
reason,  that the exchange rate will improve,  a Series may hold such currencies
for an indefinite period of time.
 
6.  ADDITIONAL RISK FACTORS
 
    OPTIONS, FUTURES CONTRACTS  AND FORWARD CONTRACTS:  Although certain  Series
will  enter into transactions in options,  Futures Contracts, Options on Futures
Contracts, Forward  Contracts  and Options  on  Foreign Currencies  for  hedging
purposes,  such transactions nevertheless involve  certain risks. For example, a
lack of  correlation between  the  instrument underlying  an option  or  Futures
Contract  and the  assets being hedged,  or unexpected  adverse price movements,
could render a Series' hedging strategy unsuccessful and could result in losses.
Certain Series also may enter  into transactions in options, Futures  Contracts,
Options  on  Futures  Contracts and  Forward  Contracts for  other  than hedging
purposes, which  involves greater  risk. In  particular, such  transactions  may
result  in losses for a Series which are  not offset by gains on other portfolio
positions, thereby reducing gross income. In addition, foreign currency  markets
may be extremely volatile from time to time. There also can be no assurance that
a  liquid secondary market will exist for  any contract purchased or sold, and a
Series may be  required to  maintain a  position until  exercise or  expiration,
which  could result in losses. The SAI  contains a description of the nature and
trading mechanics of options, Futures  Contracts, Options on Futures  Contracts,
Forward  Contracts and Options on Foreign  Currencies, and includes a discussion
of the risks related to transactions therein.
 
    Transactions  in  Forward  Contracts  may  be  entered  into  only  in   the
over-the-counter  market. Futures Contracts and Options on Futures Contracts may
be entered into  on U.S. exchanges  regulated by the  Commodity Futures  Trading
Commission  and on  foreign exchanges. In  addition, the  securities and indexes
underlying options, Futures Contracts and Options on Futures Contracts traded by
the Series will include both domestic and foreign securities.
 
    LOWER RATED BONDS: Each of the Emerging Growth Series, the Value Series, the
Research Series  and  the  Total  Return  Series  may  invest  in  fixed  income
securities  rated Baa by Moody's  or BBB by S&P  or Fitch and comparable unrated
 
                                       20
<PAGE>
securities. These  securities,  while normally  exhibiting  adequate  protection
parameters,  have speculative characteristics and changes in economic conditions
or other circumstances are more  likely to lead to  a weakened capacity to  make
principal and interest payments than in the case of higher grade securities.
 
    Each  of these  Series may also  invest in  securities rated Ba  or lower by
Moody's or  BB  or lower  by  S&P or  Fitch  and comparable  unrated  securities
(commonly  known as "junk bonds") to the  extent described above. See Appendix A
to this Prospectus  for a  description of  these ratings.  These securities  are
considered  speculative  and,  while  generally  providing  greater  income than
investments in higher rated securities,  will involve greater risk of  principal
and income (including the possibility of default or bankruptcy of the issuers of
such  securities) and may involve greater volatility of price (especially during
periods of economic uncertainty or change) than securities in the higher  rating
categories.  However, since yields  vary over time, no  specific level of income
can ever be  assured. These lower  rated high yielding  fixed income  securities
generally tend to reflect economic changes and short-term corporate and industry
developments  to  a  greater extent  than  higher rated  securities  which react
primarily to fluctuations in the general level of interest rates (although these
lower rated fixed  income securities are  also affected by  changes in  interest
rates,  the market's  perception of  their credit  quality, and  the outlook for
economic growth). In  the past, economic  downturns or an  increase in  interest
rates have, under certain circumstances, caused a higher incidence of default by
the  issuers of these securities and may do  so in the future, especially in the
case of highly leveraged issuers. During certain periods, the higher yields on a
Series' lower rated  high yielding  fixed income securities  are paid  primarily
because of the increased risk of loss of principal and income, arising from such
factors as the heightened possibility of default or bankruptcy of the issuers of
such  securities. Due to the fixed income payments of these securities, a Series
may continue to earn the same level of interest income while its net asset value
declines due  to portfolio  losses, which  could result  in an  increase in  the
Series'  yield despite the actual loss of  principal. The market for these lower
rated fixed income securities may be less liquid than the market for  investment
grade  fixed income securities, and judgment may at times play a greater role in
valuing these  securities than  in the  case of  investment grade  fixed  income
securities.  Changes in the value of  securities subsequent to their acquisition
will not  affect cash  income or  yield  to maturity  to a  Series but  will  be
reflected  in the net asset value of shares  of the Series. See the SAI for more
information on lower rated securities.
 
    FOREIGN SECURITIES: Each of the Series may invest in dollar-denominated  and
non-dollar/denominated  foreign securities.  Investing in  securities of foreign
issuers generally involves  risks not  ordinarily associated  with investing  in
securities  of  domestic  issuers.  These  include  changes  in  currency rates,
exchange  control  regulations,  governmental  administration  or  economic   or
monetary  policy (in  the U.S. or  abroad) or circumstances  in dealings between
nations. Costs may be  incurred in connection  with conversions between  various
currencies.  Special considerations  may also  include more  limited information
about foreign issuers,  higher brokerage costs,  different accounting  standards
and thinner trading markets. Foreign securities markets may also be less liquid,
more  volatile and  less subject  to government  supervision than  in the United
States. Investments  in foreign  countries could  be affected  by other  factors
including  expropriation,  confiscatory taxation  and potential  difficulties in
enforcing contractual obligations  and could be  subject to extended  settlement
periods. All of the Series may hold foreign currency received in connection with
investments in foreign securities when, in the judgment of the Adviser, it would
be  beneficial to convert such currency into U.S. dollars at a later date, based
on anticipated changes in the relevant exchange rate. Such Series may also  hold
foreign  currency in anticipation of purchasing  foreign securities. See the SAI
for further  discussion  of  foreign  securities  and  the  holding  of  foreign
currency, as well as the associated risks.
 
    AMERICAN  DEPOSITARY RECEIPTS: Each of the  Series may invest in ADRs, which
are certificates issued by  a U.S. depository (usually  a bank) and represent  a
specified  quantity of shares of an underlying  non-U.S. stock on deposit with a
custodian bank as collateral. Because  ADRs trade on U.S. securities  exchanges,
the Adviser does not treat them as foreign securities. However, they are subject
to many of the risks of foreign securities such as changes in exchange rates and
more limited information about foreign issuers.
 
                                       21
<PAGE>
    EMERGING  MARKET  SECURITIES:  Each of  the  Series may  invest  in emerging
markets. In addition to  the general risks of  investing in foreign  securities,
investments  in  emerging  markets  involve special  risks.  Securities  of many
issuers in emerging markets may be less liquid and more volatile than securities
of comparable domestic issuers. These  securities may be considered  speculative
and,  while  generally  offering higher  income  and the  potential  for capital
appreciation, may present significantly greater risk. Emerging markets may  have
different clearance and settlement procedures, and in certain markets there have
been  times when settlements  have been unable  to keep pace  with the volume of
securities transactions,  making  it  difficult to  conduct  such  transactions.
Delays  in settlement could  result in temporary  periods when a  portion of the
assets of a Series is uninvested and no return is earned thereon. The  inability
of a Series to make intended security purchases due to settlement problems could
cause a Series to miss attractive investment opportunities. Inability to dispose
of  portfolio securities due to settlement problems  could result in losses to a
Series due  to subsequent  declines  in value  of  the portfolio  securities,  a
decrease  in the level of  liquidity in a Series' portfolio,  or if a Series has
entered into  a  contract  to  sell the  security,  possible  liability  to  the
purchaser.  Certain markets may require  payment for securities before delivery,
and in such  markets a Series  bears the risk  that the securities  will not  be
delivered  and that the Series' payments will not be returned. Securities prices
in emerging  markets  can  be  significantly more  volatile  than  in  the  more
developed  nations  of  the  world,  reflecting  the  greater  uncertainties  of
investing in less  established markets and  economies. In particular,  countries
with emerging markets may have relatively unstable governments, present the risk
of   nationalization  of  businesses,  restrictions  on  foreign  ownership,  or
prohibitions of repatriation of assets, and may have less protection of property
rights than more developed countries.  The economies of countries with  emerging
markets  may be  predominantly based  on only  a few  industries, may  be highly
vulnerable to changes in local or  global trade conditions, and may suffer  from
extreme  and volatile debt burdens or  inflation rates. Local securities markets
may trade a small number of securities and may be unable to respond  effectively
to  increases  in  trading  volume,  potentially  making  prompt  liquidation of
substantial holdings difficult  or impossible  at times.  Securities of  issuers
located  in countries with  emerging markets may  have limited marketability and
may be subject to more abrupt or erratic movements.
 
    Certain  emerging  markets  may   require  governmental  approval  for   the
repatriation  of  investment  income,  capital  or  the  proceeds  of  sales  of
securities by foreign investors.  In addition, if a  deterioration occurs in  an
emerging  market's balance  of payments  or for  other reasons,  a country could
impose temporary restrictions on foreign capital remittances. A Series could  be
adversely   affected  by  delays  in,  or  a  refusal  to  grant,  any  required
governmental approval for repatriation of capital, as well as by the application
to the Series of any restrictions on investments.
 
    Investment in  certain  foreign  emerging market  debt  obligations  may  be
restricted  or controlled to varying degrees. These restrictions or controls may
at times preclude investment in certain foreign emerging market debt obligations
and increase the expenses of a Series.
 
    NON-DIVERSIFICATION: The World Governments  Series is "non-diversified,"  as
that  term is defined in  the Investment Company Act of  1940 ( the "1940 Act"),
but intends to qualify as a  "regulated investment company" ("RIC") for  federal
income  tax purposes. This means, in general,  that although more than 5% of the
Series' total assets may be invested in the securities of one issuer  (including
a  foreign government),  at the close  of each  quarter of its  taxable year the
aggregate amount of such holdings may not  exceed 50% of the value of its  total
assets, and no more than 25% of the value of its total assets may be invested in
the  securities of a single issuer. To  the extent that a non-diversified Series
at times may hold the securities of a smaller number of issuers than if it  were
"diversified"  (as defined in  the 1940 Act),  the Series will  at such times be
subject to greater  risk with respect  to its portfolio  securities than a  fund
that  invests in a broader range of securities, because changes in the financial
condition or market assessment of a single issuer may cause greater fluctuations
in the Series' total return and the net asset value of its shares.
                              -------------------
 
SHORT-TERM INVESTMENTS FOR  TEMPORARY DEFENSIVE  PURPOSES --  During periods  of
unusual market conditions when the Adviser believes that investing for temporary
defensive  purposes is appropriate,  or in order  to meet anticipated redemption
 
                                       22
<PAGE>
requests, a large portion or all of the assets of each Series may be invested in
cash (including foreign currency) or cash equivalents including, but not limited
to,  obligations  of   banks  (including  certificates   of  deposit,   bankers'
acceptances,   time  deposits  and  repurchase  agreements),  commercial  paper,
short-term notes, U.S. Government Securities and related repurchase agreements.
 
PORTFOLIO TRADING
 
    Each  Series  intends  to  manage  its  portfolio  by  buying  and   selling
securities,  as  well as  holding  securities to  maturity,  to help  attain its
investment objectives and policies.
 
    Each Series will engage in portfolio  trading if it believes a  transaction,
net  of  costs  (including  custodian  charges),  will  help  in  attaining  its
investment objectives. In trading portfolio  securities, a Series seeks to  take
advantage  of  market  developments,  yield disparities  and  variations  in the
creditworthiness of issuers. For  a description of the  strategies which may  be
used  by the Series in trading portfolio securities, see "Portfolio Transactions
and Brokerage Commissions" in the SAI.  The Total Return Series' portfolio  will
be  managed actively with respect to the Series' fixed income securities and the
asset allocations modified as the  Adviser deems necessary. Although the  Series
does  not  intend to  seek short-term  profits, fixed  income securities  in its
portfolio will be sold whenever the Adviser believes it is appropriate to do  so
without  regard to the length  of time the particular  asset may have been held.
With respect to its equity securities,  the Total Return Series does not  intend
to  trade in  securities for short-term  profits and  anticipates that portfolio
securities ordinarily will be held for  one year or longer. However, the  Series
will effect trades whenever it believes that changes in its portfolio securities
are appropriate.
 
    Because  the  World  Governments  Series is  expected  to  have  a portfolio
turnover rate of  over 100%, transaction  costs incurred by  the Series and  the
realized  capital gains and losses  of the Series may be  greater than that of a
fund with a lesser portfolio turnover rate.
 
    The primary consideration  in placing portfolio  security transactions  with
broker-dealers  for execution  is to obtain,  and maintain  the availability of,
execution at  the  most  favorable  prices and  in  the  most  effective  manner
possible. Consistent with the foregoing primary consideration, the Rules of Fair
Practice  of the National  Association of Securities  Dealers, Inc. (the "NASD")
and such other policies as the Trustees of the Trust may determine, the  Adviser
may  consider sales of  Contracts for which  the Trust is  an investment option,
together with sales of  shares of other investment  company clients of MFS  Fund
Distributors, Inc., the distributor of shares of the Trust and of the MFS Family
of Funds, as a factor in the selection of broker-dealers to execute each Series'
portfolio  transactions.  From  time  to time  the  Adviser  may  direct certain
portfolio transactions to broker-dealer firms which, in turn, have agreed to pay
a portion of the Series' operating expenses (e.g., fees charged by the custodian
of the Series' assets). For a  further discussion of portfolio trading, see  the
SAI.
                              -------------------
 
    The  SAI includes a  discussion of other investment  policies and listing of
specific investment restrictions  which govern the  investment policies of  each
Series.  The specific investment  restrictions listed in the  SAI may be changed
without shareholder  approval  unless indicated  otherwise  (see the  SAI).  The
Series'  investment limitations, policies and rating standards are adhered to at
the  time  of  purchase  or  utilization  of  assets;  a  subsequent  change  in
circumstances will not be considered to result in a violation of policy.
 
7.  MANAGEMENT OF THE SERIES
 
    The   Trust's  Board  of  Trustees,  as   part  of  its  overall  management
responsibility, oversees  various  organizations responsible  for  each  Series'
day-to-day management.
 
INVESTMENT ADVISER -- MFS manages each Series pursuant to an Investment Advisory
Agreement  with the  Trust on behalf  of each  Series dated April  14, 1994 (the
"Advisory Agreement"). MFS provides the Series with overall investment  advisory
and
 
                                       23
<PAGE>
administrative  services, as well as general  office facilities. Subject to such
policies as the Trustees may determine, MFS makes investment decisions for  each
Series. For its services and facilities, MFS receives a management fee, computed
and  paid  monthly, in  an amount  equal to  the following  annual rates  of the
average daily net assets of each Series:
 
<TABLE>
<CAPTION>
                                                                                                 PERCENTAGE OF THE
                                                                                                 AVERAGE DAILY NET
                                                                                                       ASSETS
SERIES                                                                                             OF EACH SERIES
- ---------------------------------------------------------------------------------------------  ----------------------
<S>                                                                                            <C>
Emerging Growth Series.......................................................................             0.75%
Value Series.................................................................................             0.75%
Research Series..............................................................................             0.75%
Total Return Series..........................................................................             0.75%
World Governments Series.....................................................................             0.75%
</TABLE>
 
    For the fiscal  year ended  December 31,  1995, MFS  received the  following
management  fees from  the Series under  the Advisory Agreement  and assumed the
following amounts of the Series' expenses (see "Expenses" below):
 
<TABLE>
<CAPTION>
                                                                                    MANAGEMENT FEE  EXPENSES ASSUMED
SERIES                                                                               PAID TO MFS         BY MFS
- ----------------------------------------------------------------------------------  --------------  ----------------
<S>                                                                                 <C>             <C>
Emerging Growth Series............................................................    $    6,262       $   15,659
Research Series...................................................................         4,424           16,913
Total Return Series...............................................................        10,826           25,092
World Governments Series..........................................................        33,869           43,311
</TABLE>
 
    The identity and background of the portfolio managers for each Series is set
forth below. Unless  indicated otherwise,  each portfolio manager  has acted  in
that capacity since the commencement of investment operations of each Series.
 
<TABLE>
<CAPTION>
SERIES                                                           PORTFOLIO MANAGERS
- -----------------------------  --------------------------------------------------------------------------------------
<S>                            <C>
Emerging Growth Series         John  W. Ballen, a Senior Vice President of MFS, has been employed by the Adviser as a
                               portfolio manager since  1984. Toni  Y. Shimura,  a Vice  President of  MFS, has  been
                               employed  by  the Adviser  as a  portfolio manager  since 1987.  Ms. Shimura  became a
                               portfolio manager of the Series on November 30, 1995.
Value Series                   John F. Brennan, Jr., a Senior Vice President of MFS, has been employed by the Adviser
                               as a portfolio manager since 1985.
Research Series                The Series is currently  managed by a committee  comprised of various equity  research
                               analysts employed by the Adviser.
Total Return Series            David  M. Calabro,  a Vice President  of MFS,  has been employed  by the  Adviser as a
                               portfolio manager since  1992. Mr. Calabro  is the head  of this portfolio  management
                               team  and a manager of the common stock  portion of the Series' portfolio. Geoffrey L.
                               Kurinsky, a  Senior Vice  President of  MFS, has  been employed  by the  Adviser as  a
                               portfolio  manager since 1987. Mr. Kurinsky is the manager of the Series' fixed income
                               securities. Judith N. Lamb, a Vice President of MFS, has been employed by the  Adviser
                               as  a portfolio manager since 1992. Ms. Lamb is the manager of the Series' convertible
                               securities. Lisa B. Nurme, a Vice President  of MFS, has been employed by the  Adviser
                               as  a portfolio manager since 1987. Ms. Nurme is a manager of the common stock portion
                               of the Series'  portfolio. Maura A.  Shaughnessy, a  Vice President of  MFS, has  been
                               employed  by  the Adviser  as a  portfolio manager  since 1991.  Ms. Shaughnessy  is a
                               manager of the common stock portion of the Series' portfolio. Each individual became a
                               portfolio manager of the Series on July 19, 1995.
World Governments Series       Stephen C. Bryant, a Senior  Vice President of the Adviser,  has been employed by  the
                               Adviser as a portfolio manager since 1987.
</TABLE>
 
                                       24
<PAGE>
    MFS  also serves as investment adviser to each of the other funds in the MFS
Family of Funds  (the "MFS  Funds") and to  MFS-Registered Trademark-  Municipal
Income Trust, MFS Multimarket Income Trust, MFS Government Markets Income Trust,
MFS  Intermediate  Income Trust,  MFS Charter  Income  Trust, MFS  Special Value
Trust, MFS Institutional Trust, MFS Union  Standard Trust, MFS/ Sun Life  Series
Trust,  Sun Growth Variable Annuity Fund, Inc. and seven variable accounts, each
of which is a  registered investment company established  by Sun Life  Assurance
Company  of Canada (U.S.) ("Sun  Life of Canada (U.S.)")  in connection with the
sale of  various fixed/variable  annuity  contracts. MFS  and its  wholly  owned
subsidiary, MFS Asset Management, Inc., provide investment advice to substantial
private clients.
 
    MFS  is America's oldest  mutual fund organization.  MFS and its predecessor
organizations have  a history  of  money management  dating  from 1924  and  the
founding  of the first mutual fund in the United States, Massachusetts Investors
Trust.  Net  assets  under   the  management  of   the  MFS  organization   were
approximately  $45.7  billion on  behalf of  approximately 2.0  million investor
accounts as of April  30, 1996. As  of such date,  the MFS organization  managed
approximately  $21.9  billion  of  assets  invested  in  equity  securities  and
approximately $19.4  billion  of assets  invested  in fixed  income  securities.
Approximately  $3.8  billion  of  the  assets managed  by  MFS  are  invested in
securities of foreign issuers and non-U.S. dollar-denominated securities of U.S.
issuers. MFS is a subsidiary  of Sun Life of Canada  (U.S.), which in turn is  a
wholly  owned subsidiary of  Sun Life Assurance Company  of Canada ("Sun Life").
The Directors of MFS are A. Keith  Brodkin, Jeffrey L. Shames, Arnold D.  Scott,
John  D. McNeil and John R. Gardner. Mr.  Brodkin is the Chairman, Mr. Shames is
the President  and  Mr. Scott  is  the Secretary  and  a Senior  Executive  Vice
President  of MFS.  Messrs. McNeil and  Gardner are the  Chairman and President,
respectively, of Sun Life. Sun Life, a mutual life insurance company, is one  of
the largest international life insurance companies and has been operating in the
United  States since 1895, establishing a  headquarters office here in 1973. The
executive officers of MFS report to the Chairman of Sun Life.
 
    A. Keith Brodkin, the Chairman  and a Director of  MFS, is the Chairman  and
President  and a Trustee of the Trust. W. Thomas London, Stephen E. Cavan, James
R. Bordewick, Jr.,  and James  O. Yost,  all of whom  are officers  of MFS,  are
officers of the Trust.
 
    MFS  has established a strategic alliance with Foreign & Colonial Management
Ltd. ("Foreign & Colonial"). Foreign  & Colonial is a  subsidiary of two of  the
world's  oldest  financial  services institutions,  the  London-based  Foreign &
Colonial Investment Trust PLC, which pioneered the idea of investment management
in 1868, and HYPO-BANK (Bayerische Hypotheken-und Weschsel-Bank AG), the  oldest
publicly  listed bank in Germany, founded in 1835. As part of this alliance, the
portfolio managers and investment  analysts of MFS and  Foreign & Colonial  will
share  their  views on  a  variety of  investment  related issues,  such  as the
economy, securities markets, portfolio securities and their issuers,  investment
recommendations,  strategies and  techniques, risk  analysis, trading strategies
and other portfolio management  matters. MFS will have  access to the  extensive
international  equity investment expertise of Foreign  & Colonial, and Foreign &
Colonial will have access to the  extensive U.S. equity investment expertise  of
MFS.  One or more MFS  investment analysts are expected  to work for an extended
period with Foreign & Colonial's  portfolio managers and investment analysts  at
their offices in London. In return, one or more Foreign & Colonial employees are
expected to work in a similar manner at MFS' Boston offices.
 
    In  certain  instances there  may  be securities  which  are suitable  for a
Series' portfolio as well as for portfolios  of other clients of MFS or  clients
of  Foreign  &  Colonial.  Some simultaneous  transactions  are  inevitable when
several clients  receive investment  advice  from MFS  and Foreign  &  Colonial,
particularly  when the same security is suitable for more than one client. While
in some cases this arrangement could have  a detrimental effect on the price  or
availability of the security as far as a Series is concerned, in other cases, it
may produce increased investment opportunities for the Series.
 
                                       25
<PAGE>
    From  time to time, the Adviser may  purchase, redeem and exchange shares of
any Series. The  purchase by  the Adviser  of shares of  a Series  may have  the
effect  of  lowering that  Series' expense  ratio, while  the redemption  by the
Adviser of shares of  a Series may  have the effect  of increasing that  Series'
expense ratio.
 
    DISTRIBUTOR   --  MFS  Fund  Distributors,  Inc.  ("MFD"),  a  wholly  owned
subsidiary of MFS, is the distributor of  shares of each Series and also  serves
as distributor for certain of the other mutual funds managed by MFS.
 
    SHAREHOLDER  SERVICING AGENT --  MFS Service Center,  Inc. (the "Shareholder
Servicing Agent"), a wholly owned  subsidiary of MFS, performs transfer  agency,
certain dividend disbursing agency and other services for each Series.
 
8.  INFORMATION CONCERNING SHARES OF EACH SERIES
 
PURCHASES AND REDEMPTIONS
 
    The  separate accounts of the Participating Insurance Companies place orders
to purchase and redeem shares of each  Series based on, among other things,  the
amount of premium payments to be invested and surrender and transfer requests to
be  effected on that day pursuant to Contracts. Orders received by the Trust are
effected on days on which the Exchange is open for trading. For orders  received
by  the Trust before  the close of  regular trading on  the Exchange (normally 4
p.m. eastern time), such purchases and redemptions of the shares of each  Series
are  effected at the respective net asset  values per share determined as of the
close of  regular  trading on  the  Exchange  on that  same  day.  Participating
Insurance  Companies shall be the designee of  the Trust for receipt of purchase
and redemption orders from Contract holders  and receipt by such designee  shall
constitute receipt by the Trust; provided that the Trust receives notice of such
order  by 9:30 a.m. eastern time on the next following day on which the Exchange
is open for trading. Payment for shares shall be by federal funds transmitted by
wire and must be received by 2:00 p.m. eastern time on the next following day on
which the Exchange  is open for  trading after the  purchase order is  received.
Redemption  proceeds shall be by federal funds  transmitted by wire and shall be
sent by 2:00 p.m. eastern time on  the next following day on which the  Exchange
is  open for trading after  the redemption order is  received. No fee is charged
the shareholders when they redeem Series shares.
 
    The offering of shares of any Series  may be suspended for a period of  time
and  each  Series reserves  the  right to  refuse  any specific  purchase order.
Purchase orders may be refused if, in the Adviser's opinion, they are of a  size
that  would disrupt the management of a  Series. The Trust may suspend the right
of redemption of shares of any Series  and may postpone payment for any  period:
(i) during which the Exchange is closed other than customary weekend and holiday
closings  or during which trading  on the Exchange is  restricted; (ii) when the
SEC determines  that a  state of  emergency  exists which  may make  payment  or
transfer  not reasonably practicable; (iii)  as the SEC may  by order permit for
the protection of the security  holders of the Trust; or  (iv) at any time  when
the  Trust may, under applicable laws, rules and regulations, suspend payment on
the redemption of its shares.
 
    Should any conflict between Contract holders arise which would require  that
a  substantial  amount  of net  assets  be  withdrawn from  any  Series, orderly
portfolio management  could be  disrupted  to the  potential detriment  of  such
Contract.
 
NET ASSET VALUE
 
    The  net asset value per share of  each Series is determined each day during
which the Exchange is open for  trading. This determination is made once  during
each  such day as of  the close of regular trading  on the Exchange by deducting
the amount of the Series' liabilities from  the value of the Series' assets  and
dividing  the  difference by  the number  of shares  of the  Series outstanding.
Values of assets in  a Series' portfolio  are determined on  the basis of  their
market or other fair value, as described in the SAI. All investments, assets and
liabilities  are expressed in U.S. dollars  based upon current currency exchange
rates.
 
DISTRIBUTIONS
 
    Substantially all of  each Series'  net investment income  for any  calendar
year  is declared as dividends  and paid to its  shareholders as dividends on an
annual basis. In addition, each Series may make one or more distributions during
the calendar year to its shareholders from any long-term capital gains, and  may
also make one or more distributions to its
 
                                       26
<PAGE>
shareholders  from short-term capital  gains. In determining  the net investment
income available  for distribution,  a Series  may rely  on projections  of  its
anticipated  net investment income  (which may include  short-term capital gains
from the sales  of securities  or other  assets, and,  if allowed  by a  Series'
investment  restrictions, premiums  from options  written), over  a longer term,
rather than its actual net investment income for the period.
 
    Shareholders of any of the Series may elect to receive dividends and capital
gain distributions in either cash or additional shares.
 
TAX STATUS
 
    Each Series of the Trust is treated as a separate entity for federal  income
tax  purposes. In  order to  minimize the taxes  each Series  would otherwise be
required to  pay, each  Series intends  to  qualify each  year as  a  "regulated
investment  company" under Subchapter M of the Internal Revenue Code of 1986, as
amended  ("the  Code"),  and  to  make  distributions  to  its  shareholders  in
accordance  with the timing requirements imposed by the Code. It is not expected
that any of the Series  will be required to pay  entity level federal income  or
excise taxes.
 
    Shares  of  the  Series  are offered  only  to  the  Participating Insurance
Companies' separate accounts  that fund Contracts.  See the applicable  Contract
prospectus  for a  discussion of  the federal  income tax  treatment of  (1) the
separate accounts that purchase  and hold Series shares  and (2) the holders  of
the  Contracts  that  are funded  through  those  accounts. In  addition  to the
diversification requirements  of Subchapter  M  of the  Code, each  Series  also
intends  to diversify its assets as required  by Code Section 817(h)(1), and the
regulations thereunder. See also "Tax Status" in the SAI.
 
DESCRIPTION OF SHARES, VOTING RIGHTS AND LIABILITIES
 
    Each Series currently has one class of shares, entitled Shares of Beneficial
Interest (without par  value). The Trust  has reserved the  right to create  and
issue  additional classes  and series  of shares,  in which  case each  class of
shares of a  series would  participate equally  in the  earnings, dividends  and
assets  attributable to that  class of that  particular series. Shareholders are
entitled to one vote for each share held, and shares of each Series are entitled
to vote  separately to  approve  investment advisory  agreements or  changes  in
investment  restrictions with respect  to that Series, but  shares of all Series
vote together  in  the  election  of  Trustees  and  selection  of  accountants.
Additionally,  each Series will vote separately on any other matter that affects
solely that Series, but  will otherwise vote together  with all other Series  on
all  other  matters.  The  Trust  does not  intend  to  hold  annual shareholder
meetings. The Declaration of Trust provides  that a Trustee may be removed  from
office  in  certain instances.  See "Description  of  Shares, Voting  Rights and
Liabilities" in the SAI.
 
    Each share of  a Series represents  an equal proportionate  interest in  the
Series  with each  share, subject to  the liabilities of  the particular Series.
Shares have  no pre-emptive  or conversion  rights. Shares  are fully  paid  and
non-assessable.  Should  a Series  be liquidated,  shareholders are  entitled to
share PRO RATA  in the net  assets available for  distribution to  shareholders.
Shares  will  remain  on  deposit  with  the  Shareholder  Servicing  Agent  and
certificates will not be issued.
 
    The Trust  is an  entity of  the  type commonly  known as  a  "Massachusetts
business  trust." Under  Massachusetts law,  shareholders of  such a  trust may,
under certain  circumstances, be  held  personally liable  as partners  for  its
obligations.  However, the  risk of  a shareholder  incurring financial  loss on
account of  shareholder liability  is  limited to  circumstances in  which  both
inadequate insurance existed (E.G., fidelity bonding and omission insurance) and
the Trust itself was unable to meet its obligations.
 
PERFORMANCE INFORMATION
 
    Each  Series' performance may be quoted in advertising in terms of yield and
total return. Performance is based on historical results and is not intended  to
indicate future performance. Performance quoted for a Series includes the effect
of  deducting that  Series' expenses, but  may not include  charges and expenses
attributable to any particular insurance  product. Excluding these charges  from
quotations of a Series' performance has the effect of increasing the performance
quoted. Performance for a Series will vary based on, among other things, changes
in  market conditions, the level of interest  rates and the level of the Series'
expenses. For further  information about  the Emerging  Growth Series,  Research
Series, Total Return
 
                                       27
<PAGE>
Series  and  World  Governments Series  performance  for the  fiscal  year ended
December 31, 1995, please see the Series' Annual Reports. A copy of these Annual
Reports may be obtained without  charge by contacting the Shareholder  Servicing
Agent (see back cover for address and phone number).
 
    OTHER  SERIES: From time to  time, quotations of a  Series' total return and
yield may  be  included  in  advertisements,  sales  literature  or  reports  to
shareholders  or prospective investors.  The total return of  a Series refers to
return assuming an investment has been held  in the Series for one year and  for
the  life of  the Series (the  ending date of  which will be  stated). The total
return quotations may  be expressed  in terms  of average  annual or  cumulative
rates  of return for all  periods quoted. Average annual  total return refers to
the average  annual  compound rate  of  return of  an  investment in  a  Series.
Cumulative  total  return  represents  the  cumulative  change  in  value  of an
investment in a Series.  Both will assume that  all dividends and capital  gains
distributions  were reinvested. The  yield of a Series  refers to net investment
income generated by a Series over a specified 30-day (or one month) period. This
income is then  "annualized." That  is, the amount  of income  generated by  the
Series  during that 30-day (or one month) period is assumed to be generated over
a 12-month period and is shown as a percentage of net asset value.
 
EXPENSES
 
    The Trust pays the compensation of the Trustees who are not officers of  MFS
and  all expenses of each Series (other than those assumed by MFS) including but
not limited to: governmental fees;  interest charges; taxes; membership dues  in
the  Investment Company Institute allocable to each Series; fees and expenses of
independent auditors, of legal counsel, and of any transfer agent, registrar  or
dividend disbursing agent of each Series; expenses of repurchasing and redeeming
shares  and servicing shareholder accounts;  expenses of preparing, printing and
mailing  prospectuses,  periodic  reports,  notices  and  proxy  statements   to
shareholders  and to governmental officers  and commissions; brokerage and other
expenses connected with  the execution,  recording and  settlement of  portfolio
security transactions; insurance premiums; fees and expenses of Investors Bank &
Trust Company, the Trust's Custodian, for all services to each Series, including
safekeeping of funds and securities and maintaining required books and accounts;
expenses  of  calculating the  net asset  value  of shares  of each  Series; and
expenses  of   shareholder  meetings.   Expenses  relating   to  the   issuance,
registration  and qualification  of shares of  each Series  and the preparation,
printing and mailing of  prospectuses are borne by  each Series except that  the
Distribution Agreement with MFD requires MFD to pay for prospectuses that are to
be  used for sales purposes. Expenses of the Trust which are not attributable to
a specific  Series are  allocated between  the Series  in a  manner believed  by
management of the Trust to be fair and equitable.
 
    MFS  has agreed  to pay until  December 31,  2004 the expenses  of the World
Governments Series such  that the  Series' aggregate operating  expenses do  not
exceed, on an annualized basis, 1.00% of its average daily net assets; provided,
however,  that this obligation may  be terminated or revised  at any time by MFS
without the consent of the Trust or the Series by notice in writing from MFS  to
the  Trust  on  behalf  of the  Series.  Such  payments by  MFS  are  subject to
reimbursement by the World Governments Series which will be accomplished by  the
payment  by the Series of an expense  reimbursement fee to MFS computed and paid
monthly at a  percentage of its  average daily net  assets for its  then-current
fiscal year, with a limitation that immediately after such payment the aggregate
operating expenses of the Series would not exceed, on an annualized basis, 1.00%
of  its average daily net assets. The expense reimbursement agreement terminates
for the World Governments Series  on the earlier of  the date on which  payments
made  thereunder  by the  Series equal  the prior  payment of  such reimbursable
expenses by MFS or December 31, 2004.
 
    MFS has agreed  to pay  expenses of  each of  the Series  (except the  World
Governments  Series)  such  that  the  respective  Series'  aggregate  operating
expenses shall not exceed,  on an annualized basis,  1.00% of the average  daily
net  assets of the respective Series from  November 2, 1994 through December 31,
1996, 1.25%  of the  average daily  net  assets of  the respective  Series  from
January  1, 1997 through December  31, 1998, and 1.50%  of the average daily net
assets of the respective Series from January 1, 1999 through December 31,  2004;
provided, however, that this obligation may be terminated or revised at any time
by  MFS without the consent of the Trust or the Series by notice in writing from
MFS to the Trust on  behalf of the Series. Such  payments by MFS are subject  to
reimbursement by each Series which will be
 
                                       28
<PAGE>
accomplished by the payment of the Series of an expense reimbursement fee to MFS
computed  and paid  monthly at  a percentage  of the  respective Series' average
daily net  assets for  its  then-current fiscal  year,  with a  limitation  that
immediately   after  such  payment  the  aggregate  operating  expenses  of  the
respective Series would not exceed, on an annualized basis, 1.00% of the average
daily net assets of  the respective Series through  December 31, 1996, 1.25%  of
the  average daily  net assets  of the  respective Series  from January  1, 1997
through December 31,  1998, and 1.50%  of the  average daily net  assets of  the
respective  Series from January 1, 1999  through December 31, 2004. This expense
reimbursement agreement terminates for  each such Series on  the earlier of  the
date  on which payments made thereafter by the respective Series equal the prior
payment of such reimbursable expenses by MFS or December 31, 2004.
 
SHAREHOLDER COMMUNICATIONS
 
    Owners of Contracts  issued by Participating  Insurance Companies for  which
shares  of one or more  Series are the investment  vehicle will receive from the
Participating Insurance Companies semi-annual  financial statements and  audited
year-end  financial statements  certified by  the Trust's  independent certified
public accountants. Each report will show the investments owned by the Trust and
the valuations thereof  as determined  by the  Trustees and  will provide  other
information about the Trust and its operations.
 
    Participating  Insurance Companies  with inquiries  regarding the  Trust may
call the Trust's Shareholder  Servicing Agent. (See back  cover for address  and
phone number.)
 
                              -------------------
 
    The  SAI for  the Trust, dated  May 1, 1996,  as revised August  1, 1996, as
amended or supplemented from  time to time,  contains more detailed  information
about  each of the Series, including  information related to: (i) the investment
policies and  restrictions  of each  Series;  (ii) the  Trustees,  officers  and
investment  adviser of the Trust; (iii)  portfolio transactions; (iv) the shares
of each Series, including rights and liabilities of shareholders; (v) the method
used to calculate yield and total rate of return quotations of each Series; (vi)
the determination of net asset value  of shares of each Series; (vii)  financial
statements;  (viii)  tax  considerations;  and  (ix)  certain  voting  rights of
shareholders of each Series.
 
                                       29
<PAGE>
                                                                      APPENDIX A
 
                          DESCRIPTION OF BOND RATINGS
 
The ratings of Moody's, S&P and Fitch represent their opinions as to the quality
of  various debt instruments. It should be emphasized, however, that ratings are
not absolute standards of quality. Consequently, debt instruments with the  same
maturity,  coupon and rating may have different yields while debt instruments of
the same maturity and coupon with different ratings may have the same yield.
 
                        MOODY'S INVESTORS SERVICE, INC.
 
    AAA: Bonds which are rated  Aaa are judged to be  of the best quality.  They
carry  the smallest degree of  investment risk and are  generally referred to as
"gilt edged." Interest payments are protected by a large or by an  exceptionally
stable margin and principal is secure. While the various protective elements are
likely  to change, such changes as can be visualized are most unlikely to impair
the fundamentally strong position of such issues.
 
    AA: Bonds  which are  rated Aa  are  judged to  be of  high quality  by  all
standards. Together with the Aaa group they comprise what are generally known as
high  grade bonds. They are  rated lower than the  best bonds because margins of
protection may  not  be  as  large  as in  Aaa  securities  or  fluctuations  of
protective  elements may be of greater amplitude  or there may be other elements
present which  make the  long-term  risks appear  somewhat  larger than  in  Aaa
securities.
 
    A:  Bonds which are rated A possess many favorable investment attributes and
are to be considered as upper-medium-grade obligations. Factors giving  security
to  principal and interest are considered  adequate, but elements may be present
which suggest a susceptibility to impairment sometime in the future.
 
    BAA: Bonds which are  rated Baa are  considered as medium-grade  obligations
(I.E.,  they are neither highly protected nor poorly secured). Interest payments
and principal security appear  adequate for the  present but certain  protective
elements  may be lacking or may  be characteristically unreliable over any great
length of time. Such  bonds lack outstanding  investment characteristics and  in
fact have speculative characteristics as well.
 
    BA:  Bonds which are rated Ba are judged to have speculative elements; their
future cannot be considered  as well-assured. Often  the protection of  interest
and  principal payments  may be very  moderate and thereby  not well safeguarded
during both  good  and  bad  times over  the  future.  Uncertainty  of  position
characterizes bonds in this class.
 
    B:  Bonds which are rated B  generally lack characteristics of the desirable
investment. Assurance of interest  and principal payments  or of maintenance  of
other terms of the contract over any long period of time may be small.
 
    CAA:  Bonds which are rated Caa are of  poor standing. Such issues may be in
default or there may be present elements of danger with respect to principal  or
interest.
 
    CA:  Bonds which are rated Ca represent obligations which are speculative in
a  high  degree.  Such  issues  are  often  in  default  or  have  other  marked
shortcomings.
 
    C: Bonds which are rated C are the lowest rated class of bonds and issues so
rated  can be regarded as having extremely  poor prospects of ever attaining any
real investment standing.
 
    ABSENCE OF RATING: Where no rating has  been assigned or where a rating  has
been  suspended or withdrawn, it may be  for reasons unrelated to the quality of
the issue.
 
    Should no rating be assigned, the reason may be one of the following:
 
    1.  an application for rating was not received or accepted;
 
    2.  the issue or issuer belongs  to a group of securities or companies  that
       are not rated as a matter of policy;
 
                                      A-1
<PAGE>
    3.  there is a lack of essential data pertaining to the issue or issuer; or
 
    4.    the  issue was  privately  placed, in  which  case the  rating  is not
       published in Moody's publications.
 
    Suspension or withdrawal may occur if new and material circumstances  arise,
the  effects  of which  preclude satisfactory  analysis; if  there is  no longer
available reasonable up-to-date  data to permit  a judgment to  be formed; if  a
bond is called for redemption; or for other reasons.
 
                       STANDARD & POOR'S RATINGS SERVICES
 
    AAA:  Debt rated AAA has the highest rating assigned by S&P. Capacity to pay
interest and repay principal is extremely strong.
 
    AA: Debt rated  AA has  a very  strong capacity  to pay  interest and  repay
principal and differs from the highest rated issues only in small degree.
 
    A:  Debt rated A has a strong  capacity to pay interest and repay principal,
although it is somewhat  more susceptible to the  adverse effects of changes  in
circumstances and economic conditions than debt in higher-rated categories.
 
    BBB:  Debt  rated BBB  is regarded  as  having an  adequate capacity  to pay
interest and repay principal. Whereas  it normally exhibits adequate  protection
parameters,  adverse  economic  conditions or  changing  circumstances  are more
likely to lead to a  weakened capacity to pay  interest and repay principal  for
debt in this category than in higher-rated categories.
 
    BB:  Debt rated  BB has less  near-term vulnerability to  default than other
speculative issues. However, it faces major ongoing uncertainties or exposure to
adverse  business,  financial,  or  economic  conditions  which  could  lead  to
inadequate  capacity  to meet  timely interest  and  principal payments.  The BB
rating category  is also  used for  debt  subordinated to  senior debt  that  is
assigned an actual or implied BBB- rating.
 
    B: Debt rated B has a greater vulnerability to default but currently has the
capacity  to meet interest payments  and principal repayments. Adverse business,
financial or economic conditions will  likely impair capacity or willingness  to
pay  interest and repay principal.  The B rating category  is also used for debt
subordinated to senior  debt that is  assigned an  actual or implied  BB or  BB-
rating.
 
    CCC:  Debt rated CCC has a  currently identifiable vulnerability to default,
and is dependent upon favorable  business, financial and economic conditions  to
meet  timely payment  of interest  and repayment of  principal. In  the event of
adverse business, financial, or  economic conditions, it is  not likely to  have
the  capacity to pay  interest and repay  principal. The CCC  rating category is
also used for debt  subordinated to senior  debt that is  assigned an actual  or
implied B or B- rating.
 
    CC:  The rating CC is typically applied  to debt subordinated to senior debt
that is assigned an actual or implied CCC rating.
 
    C: The rating  C is typically  applied to debt  subordinated to senior  debt
which  is assigned an  actual or implied CCC-  debt rating. The  C rating may be
used to cover a situation where a  bankruptcy petition has been filed, but  debt
service payments are continued.
 
    CI: The rating CI is reserved for income bonds on which no interest is being
paid.
 
    D:  Debt rated D is  in payment default. The D  rating category is used when
interest payments or principal payments  are not made on  the date due, even  if
the  applicable  grace period  has not  expired, unless  S&P believes  that such
payments will be made during such grace  period. The D rating also will be  used
upon  the  filing  of  a  bankruptcy  petition  if  debt  service  payments  are
jeopardized.
 
                                      A-2
<PAGE>
    PLUS (+) OR MINUS  (-): The ratings from  AA to CCC may  be modified by  the
addition  of a  plus or minus  sign to  show relative standing  within the major
rating categories.
 
    NR: Indicates  that no  public  rating has  been  requested, that  there  is
insufficient  information on which to base a rating, or that S&P does not rate a
particular type of obligation as a matter of policy.
 
A-1 AND P-1 COMMERCIAL PAPER RATINGS
 
Description of S&P, Fitch and Moody's highest commercial paper ratings:
 
    The rating "A" is  the highest commercial paper  rating assigned by S&P  and
Fitch,  and issues  so rated  are regarded as  having the  greatest capacity for
timely payment. Issues in the "A" category are delineated with the numbers 1,  2
and  3 to indicate the relative degree  of safety. The A-1 designation indicates
that the degree  of safety regarding  timely payment is  either overwhelming  or
very  strong.  Those  A-1  issues  determined  to  possess  overwhelming  safety
characteristics will be denoted with a plus (+) sign designation.
 
    The rating P-1 is the highest  commercial paper rating assigned by  Moody's.
Issuers  rated P-1 have a superior ability for repayment. P-1 repayment capacity
will normally be evidenced by the following characteristics: (1) leading  market
positions  in well  established industries;  (2) high  rates of  return on funds
employed; (3) conservative  capitalization structure with  moderate reliance  on
debt and ample asset protection; (4) broad margins in earnings coverage of fixed
financial  charges and high  internal cash generation;  and (5) well established
access to  a  range  of  financial markets  and  assured  sources  of  alternate
liquidity.
 
                         FITCH INVESTORS SERVICE, INC.
 
    AAA:  Bonds  considered to  be investment  grade and  of the  highest credit
quality. The obligor  has an exceptionally  strong ability to  pay interest  and
prepay  principal, which  is unlikely to  be affected  by reasonably foreseeable
events.
 
    AA: Bonds considered to be investment grade and of very high credit quality.
The obligor's  ability to  pay  interest and  repay  principal is  very  strong,
although  not quite as strong  as bonds rated 'AAA'.  Because bonds rated in the
'AAA' and 'AA' categories are not significantly vulnerable to foreseeable future
developments, short-term debt of these issuers is generally rated 'F-1+'.
 
    A: Bonds considered to be investment grade and of very high credit  quality.
The  obligor's ability to pay  interest and repay principal  is considered to be
strong, but may be more vulnerable to adverse changes in economic conditions and
circumstances than bonds with higher ratings.
 
    BBB: Bonds  considered to  be investment  grade and  of satisfactory  credit
quality. The obligor's ability to pay interest and repay principal is considered
to  be  adequate.  Adverse  changes in  economic  conditions  and circumstances,
however, are more likely to have  adverse impact on these bonds and,  therefore,
impair  timely payment. The likelihood that the ratings of these bonds will fall
below investment grade is higher than for bonds with higher ratings.
 
    BB: Bonds are considered speculative. The obligor's ability to pay  interest
and  repay  principal may  be affected  over time  by adverse  economic changes.
However, business  and  financial alternatives  can  be identified  which  could
assist the obligor in satisfying its debt service requirements.
 
    B:  Bonds are considered  highly speculative. While bonds  in this class are
currently meeting debt service requirements, the probability of continued timely
payment of  principal and  interest  reflects the  obligor's limited  margin  of
safety and the need for reasonable business and economic activity throughout the
life of the issue.
 
    CCC: Bonds have certain identifiable characteristics which, if not remedied,
may  lead to default.  The ability to meet  obligations requires an advantageous
business and economic environment.
 
                                      A-3
<PAGE>
    CC: Bonds are  minimally protected.  Default in payment  of interest  and/or
principal seems probable over time.
 
    C: Bonds are in imminent default in payment of interest of principal.
 
    PLUS(+)  MINUS(-): Plus  and minus  signs are used  with a  rating symbol to
indicate the relative position of a  credit within the rated category. Plus  and
minus signs, however, are not used in the 'AAA' category.
 
    NR: indicates that Fitch does not rate the specific issue.
 
    CONDITIONAL:  A conditional rating is  premised on the successful completion
of a project or the occurrence of a specific event.
 
    SUSPENDED: A rating is suspended when Fitch deems the amount of  information
available from the issuer to be inadequate for rating purposes.
 
    WITHDRAWN:  A rating will be withdrawn when an issue matures or is called or
refinanced, and, at Fitch's discretion, when  an issuer fails to furnish  proper
and timely information.
 
    FITCHALERT:  Ratings  are placed  on FitchAlert  to  notify investors  of an
occurrence that is likely to result in a rating change and the likely  direction
of  such  change.  These are  designated  a "Positive,"  indicating  a potential
upgrade, "Negative," for potential downgrade,  or "Evolving," where ratings  may
be lowered. FitchAlert is relatively short-term and should be resolved within 12
months.
 
                                      A-4
<PAGE>
INVESTMENT ADVISER
Massachusetts Financial Services Company
500 Boylston Street, Boston, MA 02116
(617) 954-5000
(800) 637-8730
 
DISTRIBUTOR
MFS Fund Distributors, Inc.
500 Boylston Street, Boston, MA 02116
(617) 954-5000
 
CUSTODIAN
Investors Bank & Trust Company
89 South Street, Boston, MA 02111
 
DIVIDEND DISBURSING AGENT
State Street Bank and Trust Company
225 Franklin Street, Boston, MA 02110
 
SHAREHOLDER SERVICING AGENT
MFS Service Center, Inc.
500 Boylston Street, Boston, MA 02116
Toll free: (800) 637-8730
MAILING ADDRESS:
P.O. Box 1400, Boston, MA 02104-9985
 
INDEPENDENT AUDITORS
Deloitte & Touche LLP
125 Summer Street, Boston, MA 02110
 
                                      [LOGO]
 
MFS-REGISTERED TRADEMARK- EMERGING GROWTH SERIES
MFS-REGISTERED TRADEMARK- VALUE SERIES
MFS-REGISTERED TRADEMARK- RESEARCH SERIES
MFS-REGISTERED TRADEMARK- TOTAL RETURN SERIES
MFS-REGISTERED TRADEMARK- WORLD GOVERNMENTS SERIES
 
                      ------------------------------------
 
                MFS-REGISTERED TRADEMARK- EMERGING GROWTH SERIES
                     MFS-REGISTERED TRADEMARK- VALUE SERIES
                   MFS-REGISTERED TRADEMARK- RESEARCH SERIES
                 MFS-REGISTERED TRADEMARK- TOTAL RETURN SERIES
               MFS-REGISTERED TRADEMARK- WORLD GOVERNMENTS SERIES
 
                                     [LOGO]
 
                                   PROSPECTUS
 
                                  MAY 1, 1996
                           AS REVISED AUGUST 1, 1996
 
                     500 Boylston Street, Boston, MA 02116
 
                            ------------------------


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