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                                                                   Exhibit 10.47

                                                                  Execution Copy

               THIRD AMENDED AND RESTATED REGISTRATION RIGHTS AND

                        RIGHT OF FIRST REFUSAL AGREEMENT

     This Agreement dated as of October 31, 1998 is entered into by and among
Ontogeny, Inc., a Delaware corporation (the "Company"), and the entities and
persons set forth on Schedule 1 (the "Purchasers").

     WHEREAS, the Company and the Purchasers desire to provide for certain
arrangements with respect to the registration of shares of capital stock of the
Company under the Securities Act of 1933 and certain rights of first refusal
with respect to future issuances of stock;

     NOW, THEREFORE, in consideration of the mutual promises and covenants
contained in this Agreement, the parties hereto agree as follows:

1.  Registration Rights.

    1.1 Certain Definitions. As used in this Agreement, the following terms
shall have the following respective meanings:

          "Commission" means the Securities and Exchange Commission, or any
other Federal agency at the time administering the Securities Act.

          "Common Stock" means the common stock, $0.01 par value per share, of
the Company.

          "Exchange Act" means the Securities Exchange Act of 1934, as amended,
or any similar Federal statute, and the rules and regulations of the Commission
issued under such Act, as they each may, from time to time, be in effect.

          "Registration Statement" means a registration statement filed by the
Company with the Commission for a public offering and sale of Common Stock
(other than a registration statement on Form S-8 or Form S-4, or their
successors, or any other form for a similar limited purpose, or any registration
statement covering only securities proposed to be issued in exchange for
securities or assets of another corporation).

          "Registration Expenses" means the expenses described in Section 1.5.

          "Registrable Shares" means (i) the shares of Common Stock issued or
issuable upon conversion of the Shares, (ii) any shares of Common Stock, and any
shares of Common Stock issued or issuable upon the conversion or exercise of any
other securities, acquired by the Purchasers pursuant to Section 2 of this
Agreement and (iii) any other shares of Common Stock issued in respect of such
shares (because of stock splits, stock dividends, reclassifications,
recapitalizations, or similar events); provided, however, that shares of Common
Stock which are Registrable Shares shall cease to be Registrable Shares (i) upon
any sale pursuant to a Registration Statement or Rule 144 under the Securities
Act or (ii) upon any sale in any manner to a person or entity which, by virtue
of Section 3 of this Agreement, is not entitled to the rights provided
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by this Agreement. Wherever reference is made in this Agreement to a request or
consent of holders of a certain percentage of Registrable Shares, the
determination of such percentage shall include shares of Common Stock issuable
upon conversion of the Shares even if such conversion has not yet been effected.

          "Securities Act" means the Securities Act of 1933, as amended, or any
similar Federal statute, and the rules and regulations of the Commission issued
under such Act, as they each may, from time to time, be in effect.

          "Shares" means (1) the shares of Series A Convertible Preferred Stock
issued pursuant to the Series A Preferred Stock Purchase Agreement dated August
26, 1994 by and among the Company and the Purchasers named therein, (2) the
shares of Series B Convertible Preferred Stock issued pursuant to the Series B
Preferred Stock Purchase Agreement dated December 13, 1995 by and among the
Company and the Purchasers named therein, (3) the shares of the Company's Series
B Convertible Preferred Stock issued or issuable to Lighthouse Capital Partners
L.P. ("Lighthouse") upon the exercise of warrants held by Lighthouse, (4) the
shares of Series E Convertible Preferred Stock issued pursuant to the Series E
Preferred Stock Purchase Agreement dated March 12, 1997 by and among the Company
and the Purchasers named therein and (5) the shares of Series F Convertible
Preferred Stock issued pursuant to the Series F Preferred Stock Purchase
Agreement dated October 1998 by and among the Company and the Purchasers named
therein (the "Series F Purchase Agreement").

          "Stockholders" means the Purchasers and any persons or entities to
whom the rights granted under this Agreement are transferred by any Purchasers,
their successors or assigns pursuant to Section 3 hereof.

1.2  Required Registrations.

     (a) At any time after the earlier of December 1, 2001, or six months after
the closing of the Company's first underwritten public offering of shares of
Common Stock pursuant to a Registration Statement, a Stockholder or Stockholders
holding in the aggregate at least 35% of the Registrable Shares may request, in
writing, that the Company effect the registration on Form S-1 or Form S-2 (or
any successor form) of Registrable Shares owned by such Stockholder or
Stockholders having an aggregate offering price of at least $7,500,000 (based on
the then current market price or fair value). If the holders initiating the
registration intend to distribute the Registrable Shares by means of an
underwriting, they shall so advise the Company in their request. In the event
such registration is underwritten, the right of other Stockholders to
participate shall be conditioned on such Stockholders' participation in such
underwriting. Upon receipt of any such request, the Company shall promptly give
written notice of such proposed registration to an Stockholders. Such
Stockholders shall have the right, by giving written notice to the Company
within 30 days after the Company provides its notice, to elect to have included
in such registration such of their Registrable Shares as such Stockholders may
request in such notice of election; provided that if the underwriter (if any)
managing the offering determines that, because of marketing factors, all of the
Registrable Shares requested to be registered by all Stockholders may not be
included in the offering, then all Stockholders who have requested registration
shall participate in the registration pro rata based upon their total ownership
of shares of Common Stock (giving effect to the conversion into Common Stock of

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all securities convertible thereunto). For purposes of making any such
reduction, each Purchaser which is a partnership, together with the affiliates,
partners and retired partners of such Purchaser, the estates and family members
of any such partners and retired partners and of their spouses, and any trusts
for the benefit of any of the foregoing persons shall be deemed to be a single
"holder," and any pro-rata reduction with respect to such "holder" shall be
based upon the aggregate amount of Registrable Shares owned by all entities and
individuals included in such "holder," as defined in this sentence (and the
aggregate amount so allocated to such "holder" shall be allocated among the
entities and individuals included in such "holder" in such manner as such
Purchaser may reasonably determine). Thereupon, the Company shall, as
expeditiously as possible, use its best efforts to effect the registration on
Form S-1 or Form S-2 (or any successor form) of all Registrable Shares which the
Company has been requested to so register.

        (b) At any time after the Company becomes eligible to file a
Registration Statement on Form S-3 (or any successor form relating to secondary
offerings), a Stockholder or Stockholders may request the Company, in writing,
to effect the registration on Form S-3 (or such successor form), of Registrable
Shares having an aggregate offering price of at least $500,000 (based on the
then current public market price). Upon receipt of any such request, the Company
shall promptly give written notice of such proposed registration to all
Stockholders. Such Stockholders shall have the right, by giving written notice
to the Company within 30 days after the Company provides its notice, to elect to
have included in such registration such of their Registrable Shares as such
Stockholders may request in such notice of election; provided that if the
underwriter (if any) managing the offering determines that, because of marketing
factors, an of the Registrable Shares requested to be registered by all
Stockholders may not be included in the offering, then all Stockholders who have
requested registration shall participate in the registration pro rata based upon
their total ownership of shares of Common Stock (giving effect to the conversion
into Common Stock of all securities convertible thereunto). For purposes of
making any such reduction, each Purchaser which is a partnership, together with
the affiliates, partners and retired partners of such Purchaser, the estates and
family members of any such partners and retired partners and of their spouses,
and any trusts for the benefit of any of the foregoing persons shall be deemed
to be a single "holder," and any pro-rata reduction with respect to such
"holder" shall be based upon the aggregate amount of Registrable Shares owned by
all entities and individuals included in such "holder," as defined in this
sentence (and the aggregate amount so allocated to such "holder" shall be
allocated among the entities and individuals included in such "holder" in such
manner as such Purchaser may reasonably determine). Thereupon, the Company
shall, as expeditiously as possible, use its best efforts to effect the
registration on Form S-3 (or such successor form) of all Registrable Shares
which the Company has been requested to so register. The Stockholders shall be
entitled to an unlimited number of registrations pursuant to this paragraph (b),
subject to the limitations described above.

        (c) The Company shall not be required to effect more than two
registrations pursuant to paragraph (a) above.

        (d) If at the time of any request to register Registrable Shares
pursuant to this Section 1.2, the Company is engaged or has fixed plans to
engage within 30 days of the time of the request in a registered public offering
as to which the Stockholders may include Registrable Shares pursuant to Section
1.3 or is engaged in any other activity which, in the good

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faith determination of the Company's Board of Directors, would be adversely
affected by the requested registration to the material detriment of the Company,
then the Company may at its option direct that such request be delayed for a
period not in excess of 120 days from the effective date of such offering or the
date of commencement of such other material activity, as the case may be, such
right to delay a request to be exercised by the Company not more than once in
any two-year period.

    1.3  Incidental Registration.

        (a) Whenever the Company proposes to file a Registration Statement
(other than pursuant to Section 1.2) at any time and from time to time, it will,
prior to such filing, give written notice to all Stockholders of its intention
to do so and, upon the written request of a Stockholder or Stockholders given
within 20 days after the Company provides such notice (which request shall state
the intended method of disposition of such Registrable Shares), the Company
shall use its best efforts to cause all Registrable Shares which the Company has
been requested by such Stockholder or Stockholders to register to be registered
under the Securities Act to the extent necessary to permit their sale or other
disposition in accordance with the intended methods of distribution specified in
the request of such Stockholder or Stockholders; provided that the Company shall
have the right to postpone or withdraw any registration effected pursuant to
this Section 1.3 without obligation to any Stockholder.

        (b) In connection with any registration under this Section 1.3 involving
an underwriting, the Company shall not be required to include (i) any
Registrable Shares in such registration unless the holders thereof accept the
terms of the underwriting as agreed upon between the Company and the
underwriters selected by it (provided that such terms must be consistent with
this Agreement), or (ii) except in the Company's initial public offering of
Common Stock or any Registration Statement filed by the Company with the
Commission within 24 months after the closing of such initial public offering,
any Registrable Shares then eligible for resale under Rule 144(k) under the
Securities Act. If in the opinion of the managing underwriter it is appropriate
because of marketing factors to limit the number of Registrable Shares to be
included in the offering, then the Company shall be required to include in the
registration only that number of Registrable Shares, if any, which the managing
underwriter believes should be included therein; provided that no persons or
entities other than the Company, the Stockholders and persons or entities
holding registration rights granted in accordance with Section 1.10 hereof shall
be permitted to include securities in the offering and that, for any
registration effected during the one year period following the initial public
offering of the Company, the number of Registrable Shares to be included in such
offering pursuant to this Section 1.3 shall not be reduced by such managing
underwriter below twenty percent (20%) of the total number of shares of Common
Stock sold in such offering. If the number of Registrable Shares to be included
in the offering in accordance with the foregoing is less than the total number
of shares which the holders of Registrable Shares have requested to be included,
then the holders of Registrable Shares who have requested registration and other
holders of securities entitled to include them in such registration shall
participate in the registration pro rata based upon their total ownership of
shares of Common Stock (giving effect to the conversion into Common Stock of all
securities convertible thereunto). For purposes of making any such reduction,
each Purchaser which is a partnership, together with the affiliates, partners
and retired partners of such Purchaser, the estates and family members of any
such partners and retired

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partners and of their spouses, and any trusts for the benefit of any of the
foregoing persons shall be deemed to be a single "holder," and any pro-rata
reduction with respect to such "holder" shall be based upon the aggregate amount
of Registrable Shares owned by all entities and individuals included in such
"holder," as defined in this sentence (and the aggregate amount so allocated to
such "holder" shall be allocated among the entities and individuals included in
such "holder" in such manner as such Purchaser may reasonably determine). If any
holder would thus be entitled to include more securities than such holder
requested to be registered, the excess shall be allocated among other requesting
holders pro rata in the manner described in this paragraph.

        (c) The registration rights contained in this Section 1.3 shall not
apply with respect to any registration statement filed by the Company solely to
register shares of Common Stock to be sold by Biogen, Inc. or Corange
International Limited.

    1.4 Registration Procedures. If and whenever the Company is required by the
provisions of this Agreement to use its best efforts to effect the registration
of any of the Registrable Shares under the Securities Act, the Company shall:

        (a) file with the Commission a Registration Statement with respect to
such Registrable Shares and use its best efforts to cause that Registration
Statement to become and remain effective;

        (b) as expeditiously as possible prepare and file with the Commission
any amendments and supplements to the Registration Statement and the prospectus
included in the Registration Statement as may be necessary to keep the
Registration Statement effective, in the case of a firm commitment underwritten
public offering, until each underwriter has completed the distribution of all
securities purchased by it and, in the case of any other offering, until the
earlier of the sale of all Registrable Shares covered thereby or 120 days after
the effective date thereof;

        (c) as expeditiously as possible furnish to each selling Stockholder
such reasonable numbers of copies of the prospectus, including a preliminary
prospectus, in conformity with the requirements of the Securities Act, and such
other documents as the selling Stockholder may reasonably request in order to
facilitate the public sale or other disposition of the Registrable Shares owned
by the selling Stockholder; and

        (d) as expeditiously as possible use its best efforts to register or
qualify the Registrable Shares covered by the Registration Statement under the
securities or Blue Sky laws of such states as the selling Stockholders shall
reasonably request, and do any and all other acts and things that may be
necessary or desirable to enable the selling Stockholders to consummate the
public sale or other disposition in such states of the Registrable Shares owned
by the selling Stockholder; provided, however, that the Company shall not be
required in connection with this paragraph (d) to qualify as a foreign
corporation or execute a general consent to service of process in any
jurisdiction.

     If the Company has delivered preliminary or final prospectuses to the
selling Stockholders and after having done so the prospectus is amended to
comply with the requirements of the Securities Act, the Company shall promptly
notify the selling Stockholders

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and, if requested, the selling Stockholders shall immediately cease making
offers of Registrable Shares and return all prospectuses to the Company. The
Company shall promptly provide the selling Stockholders with revised
prospectuses and, following receipt of the revised prospectuses, the selling
Stockholders shall be free to resume making offers of the Registrable Shares.

    1.5 Allocation of Expenses. The Company will pay all Registration Expenses
of all registrations under this Agreement; provided, however, that if a
registration under Section 1.2 is withdrawn at the request of the Stockholders
requesting such registration (other than as a result of information concerning
the business or financial condition of the Company which is made known to the
Stockholders after the date on which such registration was requested) and if the
requesting Stockholders elect not to have such registration counted as a
registration requested under Section 1.2, the requesting Stockholders shall pay
the Registration Expenses of such registration pro rata in accordance with the
number of their Registrable Shares included in such registration. For purposes
of this Section 1.5, the term "Registration Expenses" shall mean all expenses
incurred by the Company in complying with this Agreement, including, without
limitation, all registration and filing fees, exchange listing fees, printing
expenses, fees and expenses of counsel for the Company and the fees and expenses
of one counsel selected by the selling Stockholders to represent the selling
Stockholders, state Blue Sky fees and expenses, and the expense of any special
audits incident to or required by any such registration, but excluding
underwriting discounts, selling commissions and the fees and expenses of selling
Stockholders' own counsel (other than the counsel selected to represent all
selling Stockholders).

    1.6  Indemnification and Contribution.

        (a) In the event of any registration of any of the Registrable Shares
under the Securities Act pursuant to this Agreement, the Company will indemnify
and hold harmless the seller of such Registrable Shares, each underwriter of
such Registrable Shares, and each other person, if any, who controls such seller
or underwriter within the meaning of the Securities Act or the Exchange Act
against any losses, claims, damages or liabilities, joint or several, to which
such seller, underwriter or controlling person may become subject under the
Securities Act, the Exchange Act, state securities or Blue Sky laws or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect thereof) arise out of or are based upon any untrue statement or alleged
untrue statement of any material fact contained in any Registration Statement
under which such Registrable Shares were registered under the Securities Act,
any preliminary prospectus or final prospectus contained in the Registration
Statement, or any amendment or supplement to such Registration Statement, or
arise out of or are based upon the omission or alleged omission to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading; and the Company will reimburse such seller, underwriter
and each such controlling person for any legal or any other expenses reasonably
incurred by such seller, underwriter or controlling person in connection with
investigating or defending any such loss, claim, damage, liability or action;
provided, however, that the Company will not be liable in any such case to the
extent that any such loss, claim, damage or liability arises out of or is based
upon any untrue statement or omission made in such Registration Statement,
preliminary prospectus or final prospectus, or any such amendment or supplement,
in reliance upon and in conformity with information furnished to the Company, in
writing, by or on

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behalf of such seller, underwriter or controlling person specifically for use in
the preparation thereof.

        (b) In the event of any registration of any of the Registrable Shares
under the Security Shares, severally and not jointly, will indemnify and hold
harmless the Company, each of its directors and officers and each underwriter
(if any) and each person, if any, who controls the Company or any such
underwriter within the meaning of the Securities Act or the Exchange Act,
against any losses, claims, damages or liabilities, joint or several, to which
the Company, such directors and officers, underwriter or controlling person may
become subject under the Securities Act, Exchange Act, state securities or Blue
Sky laws or otherwise, insofar as such losses, claims, damages or liabilities
(or actions in respect thereof) arise out of or are based upon any untrue
statement or alleged untrue statement of a material fact contained in any
Registration Statement under which such Registrable Shares were registered under
the Securities Act, any preliminary prospectus or final prospectus contained in
the Registration Statement, or any amendment or supplement to the Registration
Statement, or arise out of or are based upon any omission or alleged omission to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading, if the statement or omission was made in
reliance upon and in conformity with information relating to such seller
furnished in writing to the Company by or on behalf of such seller specifically
for use in connection with the preparation of such Registration Statement,
prospectus, amendment or supplement; provided, however, that the obligations of
each Stockholder hereunder shall be limited to an amount equal to the net
proceeds received by such Stockholder from Registrable Shares sold in connection
with such registration.

        (c) Each party entitled to indemnification under this Section 1.6 (the
"Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom; provided, that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or litigation, shall be
approved by the Indemnified Party (whose approval shall not be unreasonably
withheld); and, provided further that the failure of any Indemnified Party to
give notice as provided herein shall not relieve the Indemnifying Party of its
obligations under this Section 1.6. The Indemnified Party may participate in
such defense at such party's expense; provided, however, that the Indemnifying
Party shall pay such expense if representation of such Indemnified Party by the
counsel retained by the Indemnifying Party would be inappropriate due to actual
or potential differing interests between the Indemnified Party and any other
party represented by such counsel in such proceeding. No Indemnifying Party, in
the defense of any such claim or litigation shall, except with the consent of
each Indemnified Party, consent to entry of any judgment or enter into any
settlement which does not include as an unconditional term thereof the giving by
the claimant or plaintiff to such Indemnified Party of a release from all
liability in respect of such claim or litigation, and no Indemnified Party shall
consent to entry of any judgment or settle such claim or litigation without the
prior written consent of the Indemnifying Party.

        (d) In order to provide for just and equitable contribution to joint
liability under the Securities Act in any case in which either (i) any holder of
Registrable Shares

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exercising rights under this Agreement, or any controlling person of any such
holder, makes a claim for indemnification pursuant to this Section 1.6 but it is
judicially determined (by the entry of a final judgment or decree by a court of
competent jurisdiction and the expiration of time to appeal or the denial of the
last right of appeal) that such indemnification may not be enforced in such case
notwithstanding the fact that this Section 1.6 provides for indemnification in
such case, or (ii) contribution under the Securities Act may be required on the
part of any such selling Stockholder or any such controlling person in cir
cumstances for which indemnification is provided under this Section 1.6; then,
in each such case, the Company and such Stockholder will contribute to the
aggregate losses, claims, damages or liabilities to which they may be subject
(after contribution from others) in such proportions so that such holder is
responsible for the portion represented by the percentage that the public
offering price of its Registrable Shares offered by the Registration Statement
bears to the public offering price of all securities offered by such
Registration Statement, and the Company is responsible for the remaining
portion; provided, however, that, in any such case, (A) no such holder will be
required to contribute any amount in excess of the net proceeds to it of all
Registrable Shares sold by it pursuant to such Registration Statement and (B) no
person or entity guilty of fraudulent misrepresentation, within the meaning of
Section 11(f) of the Securities Act, shall be entitled to contribution from any
person or entity who is not guilty of such fraudulent misrepresentation.

    1.7 Indemnification with Respect to Underwritten Offering. In the event that
Registrable Shares are sold pursuant to a Registration Statement in an
underwritten offering pursuant to Section 1.2, the Company agrees to enter into
an underwriting agreement containing customary representations and warranties
with respect to the business and operations of an issuer of the securities being
registered and customary covenants and agreements to be performed by such
issuer, including without limitation customary provisions with respect to
indemnification by the Company of the underwriters of such offering.

    1.8 Information by Holder. Each Stockholder including Registrable Shares in
any registration shall furnish to the Company such information regarding such
Stockholder and the distribution proposed by such Stockholder as the Company may
reasonably request in writing and as shall be required in connection with any
registration, qualification or compliance referred to in this Agreement.

    1.9 "Stand-Off" Agreement. Each Stockholder, if requested by the Company and
the managing underwriter of an offering by the Company of Common Stock or other
securities of the Company pursuant to a Registration Statement, shall agree not
to sell publicly or otherwise transfer or dispose of any Registrable Shares or
other securities of the Company held by such Stockholder for a period of 180
days following the effective date of such Registration Statement; provided,
that:

        (a) such agreement shall only apply to the Registration Statement
covering the Company's initial public offering of Common Stock in an
underwritten offering; and

        (b)  all officers and directors of the Company shall enter into similar
agreements.

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    1.10  Limitations on Subsequent Registration Rights.  The Company shall not,
without the prior written consent of Stockholders holding at least 66 2/3% of
the Registrable Shares, enter into any agreement (other than this Agreement)
with any holder or prospective holder of any securities of the Company which
would allow such holder or prospective holder (a) to include securities of the
Company in any Registration Statement, unless under the terms of such agreement,
such holder or prospective holder may include such securities in any such
registration only on terms consistent with the terms set forth in Section 1.3,
or (b) to make a demand registration which could result in such registration
statement being declared effective prior to December 1, 2000.

    1.11 Rule 144 Requirements. After the earliest of (i) the closing of the
sale of securities of the Company pursuant to a Registration Statement, (ii) the
registration by the Company of a class of securities under Section 12 of the
Exchange Act or (iii) the issuance by the Company of an offering circular
pursuant to Regulation A under the Securities Act, the Company agrees to:

        (a) comply with the requirements of Rule 144(c) under the Securities Act
with respect to current public information about the Company;

        (b) use its best efforts to file with the Commission in a timely manner
all reports and other documents required of the Company under the Securities Act
and the Exchange Act (at any time after it has become subject to such reporting
requirements); and

        (c) furnish to any holder of Registrable Shares upon request (i) a
     written statement by the Company as to its compliance with the requirements
     of said Rule 144(c), and the reporting requirements of the Securities Act
     and the Exchange Act (at. any time after it has become subject to such
     reporting requirements), (ii) a copy of the most recent annual or quarterly
     report of the Company and (iii) such other reports and documents of the
     Company as such holder may reasonably request to avail itself of any
     similar rule or regulation of the Commission allowing it to sell any such
     securities without registration.

    1.12  Termination.  All of the Company's obligations to register Registrable
Shares under this Agreement shall terminate on the date seven years after the
closing of the Company's initial public offering of Common Stock pursuant to a
Registration Statement.

2.  Right of First Refusal.

    2.1 (a) The Company shall not issue, sell or exchange, agree to issue, sell
or exchange, or reserve or set aside for issuance, sale or exchange, (i) any
shares of its Common Stock, (ii) any other equity securities of the Company,
(iii) any option, warrant or other right to subscribe for, purchase or otherwise
acquire any equity securities of the Company or (iv) any debt securities
convertible into capital stock of the Company (collectively, the "Offered
Securities"), unless in each such case the Company shall have first complied
with this Section 2. The Company shall deliver to each Purchaser other than
Lighthouse (an "Eligible Purchaser") a written notice of any proposed or
intended issuance, sale or exchange of Offered Securities (the "Offer"), which
Offer shall (i) identify and describe the Offered Securities, (ii) describe the
price and other terms upon which they are to be issued, sold or exchanged, and
the number or amount

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of the Offered Securities to be issued, sold or exchanged and (iii) offer to
issue and sell to or exchange with such Eligible Purchaser (A) such portion of
the Offered Securities as the aggregate number of shares of Common Stock
issuable upon conversion of Shares then held by such Eligible Purchaser, plus
any shares of Common Stock issued upon conversion of Shares held by such
Eligible Purchaser, bears to the total number of shares of Common Stock then
outstanding (including shares issued upon conversion of then outstanding shares
of c onvertible preferred stock) (the "Basic Amount") and (B) any additional
portion of the Offered Securities offered to the Eligible Purchasers as such
Eligible Purchaser shall indicate he or it will purchase or acquire should the
other Eligible Purchasers subscribe for less than their Basic Amounts (the
"Undersubscription Amount"). Each Eligible Purchaser shall have the right, for a
period of 30 days following delivery of the Offer, to purchase or acquire, at a
price and upon the other terms specified in the Offer, the number or amount of
Offered Securities described above. The Offer by its term shall remain open and
irrevocable for such 30-day period.

        (b) To accept an Offer, in whole or in part, an Eligible Purchaser must
deliver a written notice to the Company prior to the end of the 30-day period of
the Offer, setting forth the portion of the Eligible Purchaser's Basic Amount
that such Eligible Purchaser elects to purchase and, if such Eligible Purchaser
shall elect to purchase all of its Basic Amount, the Undersubscription Amount
(if any) that such Eligible Purchaser elects to purchase (the "Notice of
Acceptance"). If the Basic Amounts subscribed for by all Eligible Purchasers are
less than the aggregate of the Basic Amounts of all Eligible Purchasers (the
"Aggregate Basic Amount"), then each Eligible Purchaser who has set forth
Undersubscription Amounts in its Notice of Acceptance shall be entitled to
purchase, in addition to the Basic Amounts subscribed for, all Undersubscription
Amounts it has subscribed for; provided, however, that should the
Undersubscription Amounts subscribed for exceed the difference between the
Aggregate Basic Amount and the Basic Amounts subscribed for (the "Available
Undersubscription Amount"), each Eligible Purchaser who has subscribed for any
Undersubscription Amount shall be entitled to purchase only that portion of the
Available Undersubscription Amount as the Undersubscription Amount subscribed
for by such Eligible Purchaser bears to the total Undersubscription Amounts
subscribed for by all Eligible Purchasers, subject to rounding by the Board of
Directors to the extent it reasonably deems necessary.

        (c) In the event that Notices of Acceptance are not given by the
Eligible Purchasers in respect of all the Offered Securities, the Company shall
have 90 days from the expiration of the period set forth in Section 2.1(a) above
to issue, sell or exchange all or any part of such Offered Securities as to
which a Notice of Acceptance has not been given by the Eligible Purchasers (the
"Refused Securities"), but only upon terms and conditions which are not more
favorable, in the aggregate, to the acquiring person or persons or less
favorable to the Company than those set forth in the Offer.

        (d) In the event the Company shall propose to sell less than all the
Refused Securities (any such sale to be in the manner and on the terms specified
in Section 2.1(c) above), then each Eligible Purchaser may, at his or its sole
option and in his or its sole discretion, reduce the number or amount of the
Offered Securities specified in its Notice of Acceptance to an amount that shall
be not less than the number or amount of the Offered Securities that the
Eligible Purchaser elected to purchase pursuant to Section 2.1(b) above
multiplied by a fraction, (i) the numerator of which shall be the number or
amount of Offered Securities the Company

                                       10
<PAGE>

actually proposes to issue, sell or exchange (including Offered Securities to be
issued or sold to Eligible Purchasers pursuant to Section 2.1(b) above prior to
such reduction) and (ii) the denominator of which shall be the amount of all
Offered Securities. In the event that any Eligible Purchaser so elects to reduce
the number or amount of Offered Securities specified in his or its Notice of
Acceptance, the Company may not issue, sell or exchange more than the reduced
number or amount of the Offered Securities unless and until such securities have
again been offered to the Eligible Purchasers in accordance with Section 2.1(a)
above.

        (e) Upon the closing of the issuance, sale or exchange of all or less
than all the Refused Securities, the Eligible Purchasers shall acquire from the
Company, and the Company shall issue to the Eligible Purchasers, the number or
amount of Offered Securities specified in the Notices of Acceptance, as reduced
pursuant to Section 2.1(d) above if the Eligible Purchasers have so elected,
upon the terms and conditions specified in the Offer. The purchase by the
Eligible Purchasers of any Offered Securities is subject in all cases to the
preparation, execution and delivery by the Company and the Eligible Purchasers
of a purchase agreement relating to such Offered Securities reasonably
satisfactory in form and substance to the Eligible Purchasers and their
respective counsel.

        (f) Any Offered Securities not acquired by the Eligible Purchasers or
other persons in accordance with Section 2.1(c) above may not be issued, sold or
exchanged until they are again offered to the Eligible Purchasers under the
procedures specified in this Agreement.

        (g) The rights of the Eligible Purchasers under this Agreement shall not
apply to:

                (1) Common Stock issued as a stock dividend to holders of Common
Stock or upon any subdivision or combination of shares of Common Stock,

                (2) the issuance of shares of Common Stock upon conversion of
outstanding shares of Preferred Stock,

                (3) shares of Common Stock, or options exercisable there for,
issuable to officers, directors, consultants and employees of the Company and
any subsidiary pursuant to any plan, agreement or arrangement approved by a vote
of not less than a majority of the Board of Directors of the Company,

                (4) securities issued solely in consideration for the
acquisition (whether by merger or otherwise) by the Company or any of its
subsidiaries of all or substantially all of the stock or assets of any other
entity,

                (5) shares of Common Stock sold by the Company in an
underwritten public offering pursuant to an effective registration statement
under the Securities Act of 1933, as amended,

                (6) shares of Common Stock, or securities convertible into
Common Stock, issued in connection with any lease financing arrangement, license
agreement or

                                       11
<PAGE>

strategic collaboration agreement, up to a maximum of 2,000,000 such shares
(following the date of this Agreement), as adjusted to take into account stock
splits, recapitalizations and the like, or

                (7) shares of Common Stock, or securities convertible into
Common Stock, issued to Biogen, Inc. pursuant to the Research and
Commercialization Agreement dated July 1, 1996, as amended, or to Corange
International Limited pursuant to the Research and Commercialization Agreement
dated September 26, 1996, as amended, or their designees.

    2.2 Termination of Section 2. The provisions of this Section 2 shall
terminate upon the earliest of the following events:

        (a) The sale of all or substantially all of the assets or business of
     the Company, by merger, sale of assets or otherwise; or

        (b) The closing of the Company's initial public offering of shares of
Common Stock pursuant to an effective registration statement under the
Securities Act of 1933, as amended, resulting in at least $10,000,000 of gross
proceeds to the Company at a minimum price of $5.00 per share (subject to
appropriate adjustment for stock splits, stock dividends, recapitalizations and
other similar events).

    2.3  Definition of Eligible Purchaser.  For purposes of this Section 2, each
Eligible Purchaser which is a partnership shall be deemed to be the holder of
all Shares and shares of Common Stock issued upon conversion of Shares held by
the affiliates, partners and retired partners of such Eligible Purchaser, the
estates and family members of any such partners and retired partners and of
their spouses, and any trusts for the benefit of any of the foregoing persons.

3.  Transfers of Rights.  This Agreement, and the rights and obligations of each
Purchaser hereunder, may be assigned by such Purchaser to any person or entity
to which Shares are transferred by such Purchaser, and such transferee shall be
deemed a "Purchaser" for purposes of this Agreement; provided that the
transferee provides written notice of such assignment to the Company and agrees
to be bound hereby.

4.  General.

        (a) Notices. All notices, requests, consents, and other communications
under this Agreement shall be in writing and shall be delivered by hand, by
reputable overnight courier (such as Federal Express) or mailed by first class
certified or registered mail, return receipt requested, postage prepaid:

     If to the Company, at 45 Moulton St., Cambridge, Massachusetts 02138,
Attention:  President, or at such other address or addresses as may have been
furnished in writing by the Company to the Purchasers, with a copy to Mark G.
Borden, Esq., Hale and Dorr LLP, 60 State Street, Boston, Massachusetts 02109;
or

     If to a Purchaser, at his or its address set forth on Schedule 1.

                                       12
<PAGE>

Notices provided in accordance with this Section 4(a) shall be deemed delivered
upon personal delivery, or one day after deposit with a reputable overnight
courier, or two business days after deposit in the mail.

        (b) Entire Agreement. This Agreement embodies the entire agreement and
understanding between the parties hereto with respect to the subject matter
hereof and supersedes all prior agreements and understandings relating to such
subject matter, including, but not limited to, that Amended and Restated
Registration Rights and Right of First Refusal Agreement dated March 12, 1997
(the "Prior Agreement").

        (c) Amendments and Waivers. Any term of this Agreement may be amended
and the observance of any term of this Agreement may be waived (either generally
or in a particular instance and either retroactively or prospectively), with the
written consent of the Company and the holders of at least 66 2/3% of the then
outstanding Registrable Shares (including shares issued upon conversion
thereof); provided, that this Agreement may be amended with the consent of the
holders of less than all Registrable Shares only in a manner which affects all
Registrable Shares in the same fashion; and further provided that no consent of
the Purchasers shall be required for an amendment pursuant to Section 4(g)
below. No waivers of or exceptions to any term, condition or provision of this
Agreement, in any one or more instances, shall be deemed to be, or construed as,
a further or continuing waiver of any such term, condition or provision. The
Eligible Purchasers hereby waive any rights they may have under the Prior
Agreement (i) to purchase any shares of Series F Convertible Preferred Stock of
the Company ("Series F Stock") in connection with any sale of Series F Stock to
the purchasers thereof under the Series F Stock Purchase Agreement dated October
__, 1998.

        (d) Counterparts. This Agreement may be executed in one or more
counterparts, each of which shall be deemed to be an original, but all of which
shall be one and the same document.

        (e) Severability. The invalidity or unenforceability of any provision of
this Agreement shall not affect the validity or enforceability of any other
provision of this Agreement.

        (f) Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the Commonwealth of Massachusetts.

        (g) Addition of Purchasers. Each Purchaser of Series F Stock of the
Company under the Series F Purchase Agreement shall become a party to this
Agreement upon the Closing of its purchase of Series F Stock thereunder and his
or its execution of a counterpart signature page to this Agreement. Promptly
after each such Closing, the Company shall update Schedule 1 hereto to reflect
the name and address of such Purchaser and the number of shares of Series F
Stock so purchased.

                    [Remainder of Page Intentionally Blank]

                                       13
<PAGE>

     IN WITNESS WHEREOF, the parties hereto -have set their hands as of the date
first written above.

COMPANY:

ONTOGENY, INC.

  /s/
--------------------------------

                 [Signature page to Third Amended and Restated

           Registration Rights and Right of First Refusal Agreement]

                                       14
<PAGE>

                                   Schedule 1

Vulcan Ventures, Inc.
110 110th Avenue, N.E., Suite 550
Bellevue, WA 98004

Charles River Partnership VI
1000 Winter Street, Suite 3300
Waltham, MA 02154

Charles River Partnership VI-A
1000 Winter Street, Suite 3300
Waltham, MA 02154

Greylock Equity Limited Partnership
One Federal Street
Boston, MA 02110-2065

Highland Capital Partners 11 Limited Partnership
One International Place
Boston, MA 02110

J.H. Whitney & Co.
630 Fifth Avenue, Suite 3200
New York, NY 10011

One Liberty Fund III L.P.
One Liberty Square
Boston, MA 02109

Sutter Hill Ventures
A California Limited Partnership
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

Tow Partners
A California Limited Partnership
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

The Wythes Living Trust
755 Page Mill Road, Suite A-200
Palo Alto CA 94304

The Anderson Living Trust
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

                                       15
<PAGE>

G. Leonard Baker, Jr.
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

The Younger Living Trust
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

James C. Gaither
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

Ronald L. Perkins
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

Gregory P. Sands
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

Ronald C. Agel
279 Marlborough Street
Boston, MA 02116

Moss Forest Venture
113 Eastpointe Circle
Madison, MS 39110

New York Life Insurance Company
51 Madison Avenue, Room 1104
Office of General Counsel

New York, NY 10010
Zaffaroni Revocable Trust 1/24/86
4005 Miranda Avenue, Suite 180
Palo Alto, California 94304

Jonathan C. Peabody
234 Congress Street
Boston, MA 02110

David I. Epstein
925 Moraga Court
Palo Alto, CA 94303

Dr. David Bradford
9 Cloud View Road
Sausalito, CA 94965

                                       16
<PAGE>

Genstar Investment Corporation
Metro Tower, Suite 1170
Foster City, CA 94404

Christopher Bogan
424 Lakeshore Lane
Chapel Hill, NC 27514

Fujigin Capital Company
Central Plaza Building, 4th Floor
1-1 Kaguragashi, Shinjuku-ku
Tokyo, JAPAN

Al-Midani Investment Company
P. O. Box 40761
Riyadh 11511
Saudi Arabia

Wells Fargo Bank, Trustee FBO SHV
M/P/T FBO Tench Coxe
Wells Fargo Employee Benefit Trust
420 Montgomery Street, 2nd Fl.
San Francisco, CA 94404
Attn: Vicki Bandel

David B. Musket
19 Fieldmont Road
Belmont, MA 02478

Gutrafin Ltd.
c/o Francis Lang
40, Egerton Crescent
London SW3 2EB
England

Ariane Health Limited, LDC
c/o Muzinich & Co., Inc.
450 Park Avenue, Suite 1804
New York, NY 10022
Attn: Kenneth A. Sorensen, Ph.D

New England Partners Capital, L.P.
1 Boston Place, Suite 2100
Boston, MA 02108

                                       17
<PAGE>

NMT New Medical Technologies
c/o New Medical Tech. Management
Gewerbestrasse 18
CH-4123 Allschwill, SWITZERLAND
Attn: Jacques F. Rejeange, CEO

Saunders Holdings, L.P.
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304
Att:   Mr. Ronald Perkins
       Mr. G. Leonard Baker, Jr.

Paul M. & Marsha R. Wythes, Trustees
 of The Wythes Living Trust
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304
Att: Mr. Ronald Perkins

David L. Anderson
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304
     Att: Mr. Ronald Perkins
     Mr. G. Leonard Baker, Jr.

VENTURETECH, INC.
Peter Friedli
Friedli Corporate Finance
Freigutstrasse 5
8002 Zurich, Switzerland

David R. Golob
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

William H. Younger, Jr., Trustee
 of the Younger Living Trust
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304
Att: Mr. Ronald Perkins

Essex Special Growth Opportunities Fund
Essex Investment Management Co.
125 High Street, 39th Floor
Boston, MA 02110
Attn: Susan Stickells

                                       18
<PAGE>

Biocentiv Limited
c/o Mesco II Ltd.
409 Main Street
Ridgefield, CT 06877

Attn: Joel R. Mesznik
Westfield Performance Fund L.P.
Westfield Capital
One Financial Center
23rd Floor
Boston, MA 02111

SBSF Biotechnology Partners L.P.
Spears Benzak Solomon & Sarell
101 East Main Street
Suite "G", Attn: Lisa Tuckerman
Bozeman, MT 59715

SBSF BiotechnologyFund, L.P.
Spears Benzak Solomon & Sarell
101 East Main Street
Suite "G", Attn: Lisa Tuckerman
Bozeman, MT 59715

Aljandro Zaffaroni & Lida Zaffaroni,
c/o Technofyn Associates LLC
4005 Miranda Avenue, Suite 180
Palo Alto, California 94304
Attn: Gonzalo Silveira

The CIT Group/ Equity Investments, Inc.
c/o Bruce R. Schackman
The CIT Group/Venture Capital, Inc.
650 CIT Drive
Livingston, NJ 07039

Hare and Company
c/o OrbiMed Advisors LLC
767 Third Avenue, #64
New York, NY 10017
Attn: Samuel D. Isaley

Barry Kurokawa
200 Park Avenue
Suite 3900
New York, NY 10166

                                       19
<PAGE>

Comdisco, Inc.
611 North River Road
Rosemont, IL 60018

Mr. Frank Montgomery
113 Eastpointe Circle
Madison, MS 39110

Martin J.A. Dore
Finsbury Asset Management Limited
Alderman's House, Alderman's Walk
London EC2M 3XR
ENGLAND

Noram Trust
c/o James P. Conroy
c/o Windels, Marx, Davies & Ives
56 West 56th Street
New York, NY 10019

The Dr. M. Lee Pearce Foundation
11880 Bird Road, Suite 203
Miami, Florida 33175
Attn: Dr. Lee Pearce

The Dr. M. Lee Pearce Foundation
11880 Bird Road, Suite 203
Miami, Florida 33175
Attn: Dr. Lee Pearce

Bestin Worldwide, Ltd.
Faust, Rabbach, Stanger & Oppenheim
488 Madison Avenue
New York, NY 10022
Attn: David Faust

William H. Younger, Jr.
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

Eagle Constellation Fund Ltd.
c/o International Fund Administration
48 Par La Ville Road, Suite 464
Hamilton HM11, Bermuda
Att: Brian Mellow

                                       20
<PAGE>

UEMCO XI Limited Partnership
c/o Eagle Management Co.
10 Valley Drive, Greenwich Office Park
Greenwich, CT 06831
Att: William Fike

Gilde Investment Fund B.V.
c/o One Liberty Fund III, L.P.
One Liberty Square
Boston, MA 02109
Att: Mr. Ed Kania

Zaffaroni Family Partnership, LP
c/o Gonzalo Silveira
4005 Miranda Avenue, Suite 180
Palo Alto, CA 94304

SPRING TECHNOLOGY, INC.
Friedli Corporate Finance AG
Freigutstrasse 5
8002 Zurich SWITZERLAND
Attn: Christa Wagner

Dah Sing Medical Science Investments
Dah Sing Financial Holdings Ltd.
Friendship First Health & Happiness Dah
Sing Financial Holdings, Ltd.
36th Floor, Dah Sing Financial Centre
108 Gloucester Road
Hong Kong, Attn: David Hinde

Georges Muller
Avenue Montbenon 2
Lausanne
Switzerland 1003

John Simon
c/o UroMed Corporation
64 A Street
Needham, MA 02194

Daniel S. Gregory Family LTD Partnership
c/o Essex Street Associates
P. 0. Box 5600
Beverly Farms, MA 01915
Attention: Mark J. Gobeille

                                       21
<PAGE>

Lighthouse Capital Partners
100 Drake's Landing
Suite 260
Green Brae, CA 94904

Alimentaria International, Inc.
c/o Betainvest
Avenue Montbanon 2
Lausanne, 1003
SWITZERLAND

Andre LaMotte
Medical Science Partners
161 Worcester Road
Suite 301
Framingham, MA 01701

Medical Science Partners, L.P. II
c/o Joseph Lovett
161 Worcester Road, Suite 301
Framingham, MA 01701

Tench Coxe
755 Page Mill Road, Suite A-200
Palo Alto, CA 94304

ProMed Partners, L.P.
125 CambridePark Drive
Cambridge, MA 02140

                                       22
<PAGE>

                                 ONTOGENY, INC.

                 Third Amended and Restated Registration Rights

                      and Right of First Refusal Agreement

                           Counterpart Signature Page
                           --------------------------

                                October 31, 1998

Name of PURCHASER:_____________________________________________________

If an entity, jurisdiction of organization:____________________________

Address:_______________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

Signature:_____________________________________________________________

Name of Authorized Signature:__________________________________________

Title:_________________________________________________________________

                                       23<PAGE>
                                                                   Exhibit 10.48

                         REGISTRATION RIGHTS AGREEMENT

     This Agreement dated as of July 1, 1996 is entered into by and among
Biogen, Inc., a Massachusetts corporation (the "Purchaser") and Ontogeny, Inc.,
a Delaware corporation (the "Company").

     WHEREAS, the Company and the Purchasers desire to provide for certain
arrangements with respect to the registration of shares of capital stock of the
Company under the Securities Act of 1933;

     NOW, THEREFORE, in consideration of the mutual promises and covenants
contained in this Agreement, the parties hereto agree as follows:

     1. Registration Rights.

        1.1 Certain Definitions. As used in this Agreement, the following terms
shall have the following respective meanings:

        "Commission" means the Securities and Exchange Commission, or any
other Federal agency at the time administering the Securities Act.

        "Common Stock" means the common stock, $.01 par value per share,
of the Company.

        "Exchange Act" means the Securities Exchange Act of 1934, as amended,
or any similar Federal statute, and the rules and regulations of the Commission
issued under such Act, as they each may, from time to time, be in effect.

         "Registration Statement" means a registration statement filed by the
Company with the Commission for a public offering and sale of Common Stock
(other than a registration statement on Form S-8 or Form S-4, or their
successors, or any other form for a similar limited purpose, any registration
statement covering only securities proposed to be issued in exchange for
securities or assets of another corporation or any registration statement
covering only securities to be sold for the account of stockholders of the
Company).

         "Registration Expenses" means the expenses described in Section 1.5.

         "Registrable Shares" means (i) the shares of Common Stock issued or
issuable upon conversion of the Shares, (ii) any other shares of Common Stock
issued in respect of such shares (because of stock splits, stock dividends,
reclassifications, recapitalizations, or similar events); provided, however,
that shares of Common Stock which are Registrable Shares shall cease to be
Registrable Shares (i) upon any sale pursuant to a Registration Statement or
Rule 144 under the Securities Act or (ii) upon any sale in any manner to a
person or entity which, by virtue of Section 2 of this Agreement, is not
entitled to the rights provided by this Agreement.  Wherever reference is made
in this Agreement to a request or consent of holders of a certain percentage of
Registrable Shares, the determination of such percentage shall include shares of
Common Stock issuable upon conversion of the Shares even if such conversion has
not yet been effected.
<PAGE>

         "Securities Act" means the Securities Act of 1933, as amended, or any
similar Federal statute, and the rules and regulations of the Commission issued
under such Act, as they each may, from time to time, be in effect.

         "Shares" means (1) the shares of Series C Convertible Preferred Stock
issued pursuant to the Series C Preferred Stock Purchase Agreement of even date
herewith by and between the Company and the Purchaser.

         "Stockholders" means the Purchaser and any persons or entities to whom
the rights granted under this Agreement are transferred by Purchaser, pursuant
to Section 2 hereof.

        1.2  Required Registrations.

             (a) At any time after the Company becomes eligible to file a
     Registration Statement on Form S-3 (or any successor form relating to
     secondary offerings), a Stockholder or Stockholders may request the
     Company, in writing, to effect the registration on Form S-3 (or such
     successor form), of Registrable Shares having an aggregate offering price
     of at least $1,000,000 (based on the then current public market price).
     Upon receipt of any such request, the Company shall promptly give written
     notice of such proposed registration to all Stockholders. Such Stockholders
     shall have the right, by giving written notice to the Company within 30
     days after the Company provides its notice, to elect to have included in
     such registration such of their Registrable Shares as such Stockholders may
     request in such notice of election; provided that if the underwriter (if
     any) managing the offering determines that, because of marketing factors,
     all of the Registrable Shares requested to be registered by all
     Stockholders may not be included in the offering, then all Stockholders who
     have requested registration shall participate in the registration pro rata
     based upon their total ownership of shares of Common Stock (giving effect
     to the conversion into Common Stock of all securities convertible
     thereinto). Thereupon, the Company shall, as expeditiously as possible, use
     its best efforts to effect the registration on Form S-3 (or such successor
     form) of all Registrable Shares which the Company has been requested to so
     register.

                (b) The Company shall not be required to effect more than two
     registrations pursuant to paragraph (a) above.

                (c) If at the time of any request to register Registrable Shares
     pursuant to this Section 1.2, the Company is engaged or has fixed plans to
     engage within 30 days of the time of the request in a registered public
     offering as to which the Stockholders may include Registrable Shares
     pursuant to Section 1.3 or is engaged in any other activity which, in the
     good faith determination of the Company's Board of Directors, would be
     adversely affected by the requested registration to the material detriment
     of the Company, then the Company may at its option direct that such request
     be delayed for a period not in excess of six months from the effective date
     of such offering or the date of commencement of such other material
     activity, as the case may be, such right to delay a request to be exercised
     by the Company not more than once in any two-year period.

                                       2
<PAGE>

        1.3  Incidental Registration.

                (a) Whenever the Company proposes to file a Registration
Statement (other than pursuant to Section 1.2) at any time and from time to
time, it will, prior to such filing, give written notice to all Stockholders of
its intention to do so and, upon the written request of a Stockholder or
Stockholders given within 20 days after the Company provides such notice (which
request shall state the intended method of disposition of such Registrable
Shares), the Company shall use its best efforts to cause all Registrable Shares
which the Company has been requested by such Stockholder or Stockholders to
register to be registered under the Securities Act to the extent necessary to
permit their sale or other disposition in accordance with the intended methods
of distribution specified in the request of such Stockholder or Stockholders;
provided that the Company shall have the right to postpone or withdraw any
registration effected pursuant to this Section 1.3 without obligation to any
Stockholder.

                (b) In connection with any registration under this Section 1.3
involving an underwriting, the Company shall not be required to include (i) any
Registrable Shares in such registration unless the holders thereof accept the
terms of the underwriting as agreed upon between the Company and the
underwriters selected by it (provided that such terms must be consistent with
this Agreement), or (ii) except in the Company's initial public offering of
Common Stock or any Registration Statement filed by the Company with the
Commission within 24 months after the closing of such initial public offering,
any Registrable Shares then eligible for resale under Rule 144(k) under the
Securities Act. If in the opinion of the managing underwriter it is appropriate
because of marketing factors to limit the number of Registrable Shares to be
included in the offering, then the Company shall be required to include in the
registration only that number of Registrable Shares, if any, which the managing
underwriter believes should be included therein. If the number of Registrable
Shares to be included in the offering in accordance with the foregoing is less
than the total number of shares which the holders of Registrable Shares have
requested to be included, then the holders of Registrable Shares who have
requested registration and other holders of securities entitled to include them
in such registration shall participate in the registration pro rata based upon
their total ownership of shares of Common Stock (giving effect to the conversion
into Common Stock of all securities convertible thereinto). For purposes of
making any such reduction, each stockholder which is a partnership, together
with the affiliates, partners and retired partners of such stockholder, the
estates and family members of any such partners and retired partners and of
their spouses, and any trusts for the benefit of any of the foregoing persons
shall be deemed to be a single "holder", and any pro-rata reduction with respect
to such "holder" shall be based upon the aggregate amount of Registrable Shares
owned by all entities and individuals included in such "holder", as defined in
this sentence (and the aggregate amount so allocated to such "holder" shall be
allocated among the entities and individuals included in such "holder" in such
manner as such stockholder may reasonably determine). If any holder would thus
be entitled to include more securities than such holder requested to be
registered, the excess shall be allocated among other requesting holders pro
rata in the manner described in this paragraph.

                                       3
<PAGE>

        1.4 Registration Procedures. If and whenever the company is required by
the provisions of this Agreement to use its best efforts to effect the
registration of any of the Registrable Shares under the Securities Act, the
Company shall:

        (a) file with the Commission a Registration Statement with respect to
     such Registrable Shares and use its best efforts to cause that Registration
     Statement to become and remain effective;

        (b) as expeditiously as possible prepare and file with the Commission
any amendments and supplements to the Registration Statement and the prospectus
included in the Registration Statement as may be necessary to keep the
Registration Statement effective, in the case of a firm commitment underwritten
public offering, until each underwriter has completed the distribution of all
securities purchased by it and, in the case of any other offering, until the
earlier of the sale of all Registrable Shares covered thereby or 120 days after
the effective date thereof;

        (c) as expeditiously as possible furnish to each selling Stockholder
such reasonable numbers of copies of the prospectus, including a preliminary
prospectus, in conformity with the requirements of the Securities Act, and such
other documents as the selling Stockholder may reasonably request in order to
facilitate the public sale or other disposition of the Registrable Shares owned
by the selling Stockholder; and

        (d) as expeditiously as possible use its best efforts to register or
qualify the Registrable Shares covered by the Registration Statement under the
securities or Blue Sky laws of such states as the selling Stockholders shall
reasonably request, and do any and all other acts and things that may be
necessary or desirable to enable the selling Stockholders to consummate the
public sale or other disposition in such states of the Registrable Shares owned
by the selling Stockholder; provided, however, that the Company shall not be
required in connection with this paragraph (d) to qualify as a foreign
corporation or execute a general consent to service of process in any
jurisdiction.

     If the Company has delivered preliminary or final prospectuses to the
selling Stockholders and after having done so the prospectus is amended to
comply with the requirements of the Securities Act, the Company shall promptly
notify the selling Stockholders and, if requested, the selling Stockholders
shall immediately cease making offers of Registrable Shares and return all
prospectuses to the Company.  The Company shall promptly provide the selling
Stockholders with revised prospectuses and, following receipt of the revised
prospectuses, the selling Stockholders shall be free to resume making offers of
the Registrable Shares.

        1.5 Allocation of Expenses. The Company will pay all Registration
Expenses of all registrations under this Agreement; provided, however, that if a
registration under Section 1.2 is withdrawn at the request of the Stockholders
requesting such registration (other than as a result of information concerning
the business or financial condition of the Company which is made known to the
Stockholders after the date on which such registration was requested) and if the
requesting Stockholders elect not to have such registration counted as a
registration requested under Section 1.2, the requesting Stockholders shall pay
the Registration Expenses of such registration pro rata in accordance with the
number of their Registrable Shares included in such registration. For purposes
of this Section 1.5, the term "Registration Expenses" shall mean all expenses
incurred by the Company in complying with this Agreement, including, without
limitation, all registration and filing fees, exchange listing fees, printing
expenses, fees and expenses of counsel for the Company and the fees

                                       4
<PAGE>

and expenses of one counsel selected by the selling Stockholders to represent
the selling Stockholders, state Blue Sky fees and expenses, and the expense of
any special audits incident to or required by any such registration, but
excluding underwriting discounts, selling commissions and the fees and expenses
of selling Stockholders' own counsel (other than the counsel selected to
represent all selling Stockholders).

     1.6  Indemnification and Contribution.

        (a) In the event of any registration of any of the Registrable Shares
under the Securities Act pursuant to this Agreement, the Company will indemnify
and hold harmless the seller of such Registrable Shares, each underwriter of
such Registrable Shares, and each other person, if any, who controls such seller
or underwriter within the meaning of the Securities Act or the Exchange Act
against any losses, claims, damages or liabilities, joint or several, to which
such seller, underwriter or controlling person may become subject under the
Securities Act, the Exchange Act, state securities or Blue Sky laws or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect thereof) arise out of or are based upon any untrue statement or alleged
untrue statement of any material fact contained in any Registration Statement
under which such Registrable Shares were registered under the Securities Act,
any preliminary prospectus or final prospectus contained in the Registration
Statement, or any amendment or supplement to such Registration Statement, or
arise out of or are based upon the omission or alleged omission to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading; and the Company will reimburse such seller, underwriter
and each such controlling person for any legal or any other expenses reasonably
incurred by such seller, underwriter or controlling person in connection with
investigating or defending any such loss, claim, damage, liability or action;
provided, however, that the Company will not be liable in any such case to the
extent that any such loss, claim, damage or liability arises out of or is based
upon any untrue statement or omission made in such Registration Statement,
preliminary prospectus or final prospectus, or any such amendment or supplement,
in reliance upon and in conformity with information furnished to the Company, in
writing, by or on behalf of such seller, underwriter or controlling person
specifically for use in the preparation thereof.

        (b) In the event of any registration of any of the Registrable Shares
under the Securities Act pursuant to this Agreement, each seller of Registrable
Shares, severally and not jointly, will indemnify and hold harmless the Company,
each of its directors and officers and each underwriter (if any) and each
person, if any, who controls the Company or any such underwriter within the
meaning of the Securities Act or the Exchange Act, against any losses, claims,
damages or liabilities, joint or several, to which the Company, such directors
and officers, underwriter or controlling person may become subject under the
Securities Act, Exchange Act, state securities or Blue Sky laws or otherwise,
insofar as such losses, claims, damages or liabilities (or actions in respect
thereof) arise out of or are based upon any untrue statement or alleged untrue
statement of a material fact contained in any Registration Statement under which
such Registrable Shares were registered under the Securities Act, any
preliminary prospectus or final prospectus contained in the Registration
Statement, or any amendment or supplement to the Registration Statement, or
arise out of or are based upon any omission or alleged omission to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading, if the statement or omission was made in reliance upon
and in

                                       5
<PAGE>

conformity with information relating to such seller furnished in writing to the
Company by or on behalf of such seller specifically for use in connection with
the preparation of such Registration Statement, prospectus, amendment or
supplement; provided, however, that the obligations of each Stockholder
hereunder shall be limited to an amount equal to the net proceeds received by
such Stockholder from Registrable Shares sold in connection with such
registration.

        (c) Each party entitled to indemnification under this Section 1.6 (the
"Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom; provided, that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or litigation, shall be
approved by the Indemnified Party (whose approval shall not be unreasonably
withheld); and, provided, further, that the failure of any Indemnified Party to
give notice as provided herein shall not relieve the Indemnifying Party of its
obligations under this Section 1.6. The Indemnified Party may participate in
such defense at such party's expense; provided, however, that the Indemnifying
Party shall pay such expense if representation of such Indemnified Party by the
counsel retained by the Indemnifying Party would be inappropriate due to actual
or potential differing interests between the Indemnified Party and any other
party represented by such counsel in such proceeding. No Indemnifying Party, in
the defense of any such claim or litigation shall, except with the consent of
each Indemnified Party, consent to entry of any judgment or enter into any
settlement which does not include as an unconditional term thereof the giving by
the claimant or plaintiff to such Indemnified Party of a release from all
liability in respect of such claim or litigation, and no Indemnified Party shall
consent to entry of any judgment or settle such claim or litigation without the
prior written consent of the Indemnifying Party.

        (d) In order to provide for just and equitable contribution to joint
liability under the Securities Act in any case in which either (i) any holder of
Registrable Shares exercising rights under this Agreement, or any controlling
person of any such holder, makes a claim for indemnification pursuant to this
Section 1.6 but it is judicially determined (by the entry of a final judgment or
decree by a court of competent jurisdiction and the expiration of time to appeal
or the denial of the last right of appeal) that such indemnification may not be
enforced in such case notwithstanding the fact that this Section 1.6 provides
for indemnification in such case, or (ii) contribution under the Securities Act
may be required on the part of any such selling Stockholder or any such
controlling person in circumstances for which indemnification is provided under
this Section 1.6; then, in each such case, the Company and such Stockholder will
contribute to the aggregate losses, claims, damages or liabilities to which they
may be subject (after contribution from others) in such proportions so that such
holder is responsible for the portion represented by the percentage that the
public offering price of its Registrable Shares offered by the Registration
Statement bears to the public offering price of all securities offered by such
Registration Statement, and the Company is responsible for the remaining
portion; provided, however, that, in any such case, (A) no such holder will be
required to contribute any amount in excess of the net proceeds to it of all
Registrable Shares sold by it pursuant to such Registration Statement, and (B)
no person or entity guilty of fraudulent misrepresentation, within the meaning
of Section 11(f) of the Securities Act, shall be entitled to contribution from
any person or entity who is not guilty of such fraudulent misrepresentation.

                                       6
<PAGE>

        1.7 Indemnification with Respect to Underwritten Offering. In the event
that Registrable Shares are sold pursuant to a Registration Statement in an
underwritten offering pursuant to Section 1.2, the Company agrees to enter into
an underwriting agreement containing customary representations and warranties
with respect to the business and operations of an issuer of the securities being
registered and customary covenants and agreements to be performed by such
issuer, including without limitation customary provisions with respect to
indemnification by the Company of the underwriters of such offering.

        1.8 Information by Holder. Each Stockholder including Registrable Shares
in any registration shall furnish to the Company such information regarding such
Stockholder and the distribution proposed by such Stockholder as the Company may
reasonably request in writing and as shall be required in connection with any
registration, qualification or compliance referred to in this Agreement.

        1.9 "Stand-Off" Agreement. Each Stockholder, if requested by the Company
and the managing underwriter of an offering by the Company of Common Stock or
other securities of the Company pursuant to a Registration Statement, shall
agree not to sell publicly or otherwise transfer or dispose of any Registrable
Shares or other securities of the Company held by such Stockholder for a period
of 180 days following the effective date of such Registration Statement;
provided, that:

             (a) such agreement shall only apply to the Registration Statement
covering the Company's initial public offering of Common Stock in an
underwritten offering; and

             (b) all officers and directors of the Company shall enter into
similar agreements.

        1.10 Rule 144 Requirements. After the earliest of (i) the closing of the
sale of securities of the Company pursuant to a Registration Statement, (ii) the
registration by the Company of a class of securities under Section 12 of the
Exchange Act, or (iii) the issuance by the Company of an offering circular
pursuant to Regulation A under the Securities Act, the Company agrees to:

             (a) comply with the requirements of Rule 144(c) under the
Securities Act with respect to current public information about the Company;

             (b) use its best efforts to file with the Commission in a timely
manner all reports and other documents required of the Company under the
Securities Act and the Exchange Act (at any time after it has become subject to
such reporting requirements); and

             (c) furnish to any holder of Registrable Shares upon request (i) a
written statement by the Company as to its compliance with the requirements of
said Rule 144(c), and the reporting requirements of the Securities Act and the
Exchange Act (at any time after it has become subject to such reporting
requirements), (ii) a copy of the most recent annual or quarterly report of the
Company, and (iii) such other reports and documents of the Company as such
holder may reasonably request to avail itself of any similar rule or regulation
of the Commission allowing it to sell any such securities without registration.

                                       7
<PAGE>

        1.11 Termination. All of the Company's obligations to register
Registrable Shares under this Agreement shall terminate on the date seven years
after the closing of the Company's initial public offering of Common Stock
pursuant to a Registration Statement.

        2. Transfers of Rights. This Agreement, and the rights and obligations
of each Purchaser hereunder, may be assigned by such Purchaser to any person or
entity to which at least 100,000 Shares are transferred by such Purchaser, and
such transferee shall be deemed a "Purchase" for purposes of this Agreement;
provided that the transferee provides written notice of such assignment to the
Company and agrees to be bound hereby and provided further that the transferee
is not a competitor of the Company.

        3.  General.

                (a) Notices. All notices, requests, consents, and other
communications under this Agreement shall be in writing and shall be delivered
by hand or mailed by first class certified or registered mail, return receipt
requested, postage prepaid:

     If to the Company, at 45 Moulton Street, Cambridge, Massachusetts 02138,
Attention: President, or at such other address or addresses as may have been
furnished in writing by the Company to the Purchaser, with a copy to Mark G.
Borden, Esq., Hale and Dorr, 60 State Street, Boston, Massachusetts 02109; or

     If to a Purchaser, at his or its address set forth in the Series C Purchase
Agreement, or at such other address or addresses as may have been furnished to
the Company in writing by such Purchaser.

                (b) Entire Agreement. This Agreement embodies the entire
agreement and understanding between the parties hereto with respect to the
subject matter hereof and supersedes all prior agreements and understandings
relating to such subject matter.

                (c) Amendments and Waivers. Any term of this Agreement may be
amended and the observance of any term of this Agreement may be waived (either
generally or in a particular instance and either retroactively or
prospectively), with the written consent of the Company and the holders of at
least 66 2/3% of the then outstanding Registrable Shares (including shares
issued upon conversion thereof). No waivers of or exceptions to any term,
condition or provision of this Agreement, in any one or more instances, shall be
deemed to be, or construed as, a further or continuing waiver of any such term,
condition or provision.

                (d) Counterparts. This Agreement may be executed in one or more
counterparts, each of which shall be deemed to be an original, but all of which
shall be one and the same document.

                (e) Severability. The invalidity or unenforceability of any
provision of this Agreement shall not affect the validity or enforceability of
any other provision of this Agreement.

                (f) Governing Law. This Agreement shall be governed by and
construed in accordance with the laws of the Commonwealth of Massachusetts.

                                       8
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have set their hands as of the date
first written above:

                              COMPANY:

                              ONTOGENY, INC.

                              /s/ William W. Helman
                              ---------------------
                              William W. Helman, President

                              Dated:

                              PURCHASER:

                              BIOGEN, INC.

                              By:/s/ James R. Tobin
                                 ------------------

                              Dated:

                                       9

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