MFS VARIABLE INSURANCE TRUST
497, 1997-05-05
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<PAGE>
 
<TABLE>
<S>                                        <C>
MFS-REGISTERED TRADEMARK- EMERGING GROWTH
SERIES
MFS-REGISTERED TRADEMARK- TOTAL RETURN     PROSPECTUS
SERIES                                     May 1, 1997
</TABLE>
 
- --------------------------------------------------------------------------------
 
<TABLE>
<S>                                                            <C>                      <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"),  two 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; and
 
- -- 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.
                              -------------------
 
THE  EMERGING GROWTH  SERIES IS  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 THE SERIES MAY BE SUBJECT TO A GREATER DEGREE OF RISK
THAN INVESTMENTS IN OTHER INVESTMENT COMPANIES WHICH INVEST ENTIRELY IN DOMESTIC
SECURITIES.
                              -------------------
 
  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.
                              -------------------
 
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,  1997, as  amended or  supplemented from  time to  time (the  "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"). The  SEC
maintains  an Internet World Wide Web site that contains the SAI, materials that
are incorporated  by reference  into  this Prospectus  and  the SAI,  and  other
information  regarding the Series. This Prospectus is available on the Adviser's
Internet World Wide Web site at http://www.mfs.com.
 
   INVESTORS SHOULD READ THIS PROSPECTUS AND RETAIN IT FOR FUTURE REFERENCE.
<PAGE>
TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                                                                       PAGE
                                                                                                       ---
  <S>                                                                                                  <C>
  1.  Expense Summary................................................................................   3
  2.  Investment Concept of the Trust................................................................   4
  3.  Condensed Financial Information................................................................   5
  4.  Investment Objectives and Policies.............................................................   7
      MFS Emerging Growth Series.....................................................................   7
      MFS Total Return Series........................................................................   7
  5.  Investment Techniques..........................................................................   8
  6.  Additional Risk Factors........................................................................  13
  7.  Management of the Series.......................................................................  16
  8.  Information Concerning Shares of Each Series...................................................  18
      Purchases and Redemptions......................................................................  18
      Net Asset Value................................................................................  18
      Distributions..................................................................................  19
      Tax Status.....................................................................................  19
      Description of Shares, Voting Rights and Liabilities...........................................  19
      Performance Information........................................................................  20
      Expenses.......................................................................................  20
      Shareholder Communications.....................................................................  21
  Appendix A -- Description of Bond Ratings..........................................................  A-1
</TABLE>
 
                                       2
<PAGE>
1.  EXPENSE SUMMARY
 
ANNUAL OPERATING EXPENSES (AS A PERCENTAGE OF AVERAGE NET ASSETS):
 
<TABLE>
<CAPTION>
                                                                MFS        MFS
                                                              EMERGING    TOTAL
                                                               GROWTH     RETURN
                                                               SERIES     SERIES
                                                              --------   --------
<S>                                                           <C>        <C>
Management Fee..............................................  0.75%      0.75%
Other Expenses (after expense limitation)(1)(2).............  0.25%      0.25%
                                                              --------    ---
Total Operating Expenses (after expense limitation)(2)......  1.00%      1.00%
</TABLE>
 
- ------------------------
 
<TABLE>
<S>        <C>
(1)        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."
(2)        The Adviser has agreed to bear expenses for each Series, subject to reimbursement by each Series, such that  each
           Series'  "Other Expenses" shall not exceed 0.25% of the average daily net assets of the Series during the current
           fiscal year. See "Information Concerning Shares of  Each Series-- Expenses." Otherwise, "Other Expenses" for  the
           Emerging  Growth Series and the Total Return Series would  be 0.41% and 1.35%, respectively, and "Total Operating
           Expenses" would be 1.16% and 2.10%, respectively, for these Series.
</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.
 
                                       3
<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 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.
 
                                       4
<PAGE>
3.  CONDENSED FINANCIAL INFORMATION
 
The  following financial information (presented  for each Series which commenced
investment operations prior  to December 31,  1996) 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.
 
                             EMERGING GROWTH SERIES
 
<TABLE>
<CAPTION>
                                                                      YEAR ENDED          PERIOD ENDED
                                                                   DECEMBER 31, 1996   DECEMBER 31, 1995*
                                                                   -----------------   ------------------
<S>                                                                <C>                 <C>
Per share data (for a share outstanding throughout each period):
Net asset value--beginning of period.............................      $  11.41             $10.00
                                                                       --------             ------
Income from investment operations#--
  Net investment income (loss)Section............................      $  (0.01)            $ 0.01
  Net realized and unrealized gain on investments and foreign
    currency transactions........................................          1.95               1.74
                                                                       --------             ------
    Total from investment operations.............................      $   1.94             $ 1.75
                                                                       --------             ------
Less distributions declared to shareholders--
  From net investment income.....................................      $     --             $(0.01)
  From net realized gain on investments and foreign currency
    transactions.................................................         (0.06)             (0.26)
  In excess of net realized gain on investments and foreign
    currency transactions........................................         (0.05)                --
  Tax return of capital..........................................            --              (0.07)
                                                                       --------             ------
    Total distributions declared to shareholders.................      $  (0.11)            $(0.34)
                                                                       --------             ------
Net asset value--end of period...................................      $  13.24             $11.41
                                                                       --------             ------
                                                                       --------             ------
Total return.....................................................         17.02%             17.41%++
Ratios (to average net assets)/Supplemental dataSection:
  Expenses.......................................................          1.00%              1.00%+
  Net investment income (loss)...................................         (0.08)%             0.10%+
Portfolio turnover...............................................            96%                73%
Average commission rate###.......................................      $ 0.0401                 --
Net assets at end of period (000 omitted)........................      $104,956             $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.
      ###  Average commission rate is calculated for Series' with fiscal years beginning on or after September 1, 1995.
  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..............................................         $(0.03)           $(0.18)
Ratios (to average net assets):
  Expenses.......................................................           1.16%             2.91%+
  Net investment loss............................................          (0.23)%           (1.78)%+
</TABLE>
 
                                       5
<PAGE>
                              TOTAL RETURN SERIES
 
<TABLE>
<CAPTION>
                                                                       YEAR ENDED           PERIOD ENDED
                                                                    DECEMBER 31, 1996    DECEMBER 31, 1995*
                                                                   -------------------   ------------------
<S>                                                                <C>                   <C>
Per share data (for a share outstanding throughout each period):
Net asset value--beginning of period.............................        $ 12.25               $10.00
                                                                         -------               ------
Income from investment operations#--
  Net investment incomeSection...................................        $  0.46               $ 0.41
  Net realized and unrealized gain on investments and foreign
    currency transactions........................................           1.30                 2.32
                                                                         -------               ------
    Total from investment operations.............................        $  1.76               $ 2.73
                                                                         -------               ------
Less distributions declared to shareholders--
  From net investment income.....................................        $ (0.21)              $(0.25)
  From net realized gain on investments and foreign currency
    transactions.................................................          (0.09)               (0.23)
                                                                         -------               ------
    Total distributions declared to shareholders.................        $ (0.30)              $(0.48)
                                                                         -------
Net asset value--end of period...................................        $ 13.71               $12.25
                                                                         -------               ------
                                                                         -------               ------
Total return.....................................................          14.37%               27.34%++
Ratios (to average net assets)/Supplemental dataSection:
  Expenses.......................................................           1.00%                1.00%+
  Net investment income..........................................           3.59%                3.83%+
Portfolio turnover...............................................             76%                  16%
Average commission rate###.......................................        $0.0485                   --
Net assets at end of period (000 omitted)........................        $19,250               $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.
      ###  Average commission rate is calculated for funds with fiscal years beginning on or after September 1, 1995.
  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............................................            $0.32             $0.22
Ratios (to average net assets):
  Expenses.......................................................             2.10%             2.49%+
  Net investment income..........................................             2.49%             2.09%+
</TABLE>
 
                                       6
<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 fixed income
securities (which  may be  unrated), 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  Series
may   invest  in  non-convertible  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 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 5% of its net assets in  these
securities.  For  a  description  of  these  ratings,  see  Appendix  A  to this
Prospectus.
 
    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 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 non-convertible
fixed income securities, and at  least 40% and no more  than 75% of the  Series'
assets  will be  invested in equity  securities. Equity securities  in which the
Series may invest include the following: common
 
                                       7
<PAGE>
stocks, preferred  stocks  and  preference stocks;  securities  such  as  bonds,
warrants or rights that are convertible into stocks; and depositary receipts for
those securities. These securities may be listed on securities exchanges, traded
in various over-the-counter markets or have no organized markets.
 
    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.  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' non-convertible
fixed income  investments  may consist  of  both "investment  grade"  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 non-convertible  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 non-convertible fixed income  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.
 
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.
 
                                       8
<PAGE>
    BRADY  BONDS:  Each of  the  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 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
liquid assets.
 
    MORTGAGE "DOLLAR ROLL" TRANSACTIONS: The Total Return 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.  The  Series  records  these  transactions  as  sale  and  purchase
transactions,  rather than as borrowing transactions. The 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"). A determination  is made  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, retains  oversight,
focusing   on  factors  such   as  valuation,  liquidity   and  availability  of
information. Investing  in  Rule  144A  securities  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.
 
                                       9
<PAGE>
    CORPORATE  ASSET-BACKED  SECURITIES:  Each  of  the  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 Total  Return
Series  may invest in zero coupon bonds. 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. The  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.
 
    LOAN PARTICIPATIONS AND OTHER  DIRECT INDEBTEDNESS: Each  of the 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.
 
                                       10
<PAGE>
    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.
 
    MORTGAGE  PASS-THROUGH  SECURITIES: The  Total Return  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: The Total Return 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.
 
    OPTIONS ON SECURITIES: Each of the  Series may write (sell) covered put  and
call options and purchase put and call options on securities. Each of the 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 the 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.
 
                                       11
<PAGE>
    OPTIONS ON STOCK INDICES: Each of  the 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.
 
    Each of the 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: The Total Return 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 the 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
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"). The Series  may also purchase  and
write  options on such Futures Contracts  ("Options on Futures Contracts"). Each
of the Emerging Growth Series and the Total Return Series may purchase and  sell
Futures  Contracts  on stock  indices, and  may also  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.
 
                                       12
<PAGE>
    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 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 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.
 
                                       13
<PAGE>
    LOWER RATED BONDS: Each of the Series may invest in fixed income  securities
rated  Baa by Moody's or BBB by  S&P or Fitch and comparable unrated 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. Each 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.
 
    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
 
                                       14
<PAGE>
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.
                              -------------------
 
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
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.
 
                                       15
<PAGE>
    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"). Under  the Advisory  Agreement, MFS  provides the Series
with overall  investment advisory  services.  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%
Total Return Series.......................................................................             0.75%
</TABLE>
 
    For the fiscal  year ended  December 31,  1996, 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.........................................................    $  314,262       $   62,962
Total Return Series............................................................        60,979           87,721
</TABLE>
 
    MFS or its affiliates will pay  a fee to Connecticut General Life  Insurance
Company  ("CIGNA") equal, on an annualized basis,  to 0.15% of the aggregate net
assets of the Trust up to $200 million and 0.20% of the aggregate net assets  of
the Trust attributable to Contracts offered by separate accounts by CIGNA or its
affiliates.  Such fees will not be paid by the Series, their shareholders, or by
the Contract holders.
 
    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.
</TABLE>
 
                                       16
<PAGE>
<TABLE>
<CAPTION>
SERIES                                                       PORTFOLIO MANAGERS
- ------------------------  ----------------------------------------------------------------------------------------
<S>                       <C>
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.
</TABLE>
 
    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,  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  Institutional Advisers,
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 $52.8  billion on  behalf of  approximately 2.3  million  investor
accounts  as of February 28, 1997. As of such date, the MFS organization managed
approximately  $28.9  billion  of  assets  invested  in  equity  securities  and
approximately  $19.9  billion of  assets  invested in  fixed  income securities.
Approximately $4.0  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 Donald A. Stewart. 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  Stewart 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  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  has  access  to  the  extensive
international  equity investment expertise of Foreign  & Colonial, and Foreign &
Colonial has access to  the extensive U.S. equity  investment expertise of  MFS.
MFS  and Foreign Colonial each have investment personnel working in each other's
offices in Boston and London, respectively.
 
    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
 
                                       17
<PAGE>
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, however,  it  may
produce increased investment opportunities for the Series.
 
    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.
 
    ADMINISTRATOR  --  MFS  provides  the  Series  with  certain  administrative
services pursuant to a Master  Administrative Services Agreement dated March  1,
1997.  Under this  Agreement, MFS  provides the  Series with  certain financial,
legal, compliance, shareholder communications and other administrative services.
As a partial reimbursement for the cost of providing these services, the  Series
pays  MFS an administrative  fee up to  0.015% per annum  of the Series' average
daily net assets,  provided that  the administrative fee  is not  assessed on  a
Series' assets that exceed $3 billion.
 
    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
 
                                       18
<PAGE>
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 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"). Because each Series intends  to distribute all of its net
investment income and net capital gains  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.
 
                                       19
<PAGE>
    CG Variable Annuity--Separate Account II,  Hartford, CT, owns 44.85% of  the
Total Return Series, and, therefore, controls the Series.
 
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 Series' performance for the  fiscal
year  ended December 31, 1996, 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).
 
    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.
 
    Subject  to termination or revision  at the sole discretion  of MFS, MFS has
agreed to bear expenses of each of  the Series such that the respective  Series'
"Other Expenses," which are defined to include all expenses of the Series except
for  management fees, do not exceed 0.25% of the average daily net assets of the
Series (the "Maximum Percentage"). The obligation of MFS to bear these  expenses
for  a Series terminates on the last day of the Series' fiscal year in which its
"Other Expenses" are less than or equal to the Maximum Percentage. The  payments
made  by MFS  on behalf  of each  Series under  this arrangement  are subject to
reimbursement by the Series to MFS, which will be accomplished by the payment of
an expense reimbursement fee by the Series to MFS computed and paid monthly at a
percentage of the Series' average daily  net assets for its then current  fiscal
year,  with a limitation that immediately  after such payment the Series' "Other
Expenses" will not exceed the Maximum Percentage. This expense reimbursement  by
each  Series to MFS terminates on the earlier of the date on which payments made
by the Series equal the  prior payment of such  reimbursable expenses by MFS  or
December 31, 2004.
 
                                       20
<PAGE>
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, 1997,  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; and  (vii)  certain voting  rights  of
shareholders of each Series.
 
                                       21
<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;
 
    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.
 
                                      A-1
<PAGE>
    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.
 
    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:
 
                                      A-2
<PAGE>
    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.
 
    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.
 
                                      A-3
<PAGE>
    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) 343-2829, ext. 3500
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- TOTAL RETURN SERIES
                     500 Boylston Street, Boston, MA 02116
 
                      ------------------------------------
                       MFS-REGISTERED TRADEMARK- EMERGING
                                 GROWTH SERIES
 
                        MFS-REGISTERED TRADEMARK- TOTAL
                                 RETURN SERIES
 
                                     [LOGO]
 
                                   PROSPECTUS
 
                                  MAY 1, 1997
                            ------------------------


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