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                                                                   Exhibit 10.64

                               PLEDGE AGREEMENT
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     This is a pledge agreement made as of the 17th day of June, 1996 between
Doros Platika ("Pledgor") and Ontogeny, Inc. ("Pledgee").

     1.   Pledge of Collateral. Pledgor hereby grants Pledgee a security
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interest in the stock identified in Exhibit A, annexed hereto, which Pledgor has
delivered to Pledgee (the "Collateral").

     2.   Obligations Secured. The security interest in the Collateral granted
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hereby secures payment and performance of the promissory note from Pledgor to
Pledgee of even date herewith in the principal amount of $500,000 (the "Note"),
together with all interest on such Note (the "Obligations").

     3.   Pledgee's Rights and Duties with Respect to the Collateral. Pledgee's
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only duty with respect to the Collateral shall be to exercise reasonable care to
secure the safe custody thereof. Pledgee shall be relieved of all responsibility
for the Collateral upon surrendering it to Pledgor.

     4.   Pledgor's Warranties and Indemnity.  Pledgor represents, warrants and
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covenants (a) that he is and will be the lawful owner of the Collateral, (b)
that the Collateral is and will be fully paid and non-assessable, (c) that the
Collateral is and will remain free and clear of all liens, encumbrances and
security interests other than the security interest granted by Pledgor
hereunder, and (d) that Pledgor has the sole right and lawful authority to
pledge the Collateral and otherwise to comply with the provisions hereof. In the
event that any adverse claim is asserted in respect of the Collateral or any
portion thereof, except such as may result from an act of Pledgee not authorized
hereunder, Pledgor promises and agrees to indemnify Pledgee and hold Pledgee
harmless from and against any losses, liabilities, damages, expenses, costs and
reasonable counsel fees incurred by Pledgee in exercising any
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right, power or remedy of Pledgee hereunder or defending, protecting or
enforcing the security interests created hereunder. Any such loss, liability or
expense so incurred shall be paid by Pledgor upon demand, become part of the
Obligations secured by the Collateral and bear interest at the rate provided in
the Note until paid.

     5.   Voting of Collateral. While Pledgor is not in default hereunder,
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Pledgor may vote stock and other securities pledged as Collateral.

     6.   Dividends and Other Distributions.  While Pledgor is not in default
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hereunder, Pledgor may receive cash dividends and other distributions payable
with respect to Collateral, provided, however, that Pledgor shall immediately
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inform Pledgee of the receipt of any such dividend or other distribution and
shall hold the amount thereof in trust for Pledgee unless and until Pledgee
shall in writing release Pledgor from such trust.  Pledgor shall cause all non-
cash dividends and distributions with respect to Collateral to be distributed
directly to Pledgee, to be held by Pledgee as additional Collateral, and if any
such distribution is made to Pledgor he shall receive such distribution in trust
for Pledgee and shall immediately transfer it to Pledgee.

     7.   Pledgor's Default.  Pledgor shall be in default hereunder upon the
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occurrence of any of the following events:

          (a)  If any warranty of Pledgor hereunder is or shall become false in
any material respect;

          (b)  If Pledgor fails to fulfill any material obligation hereunder,
which is not cured within 30 days after written notice thereof; or

          (c)  If Pledgor fails to pay or perform any of the Obligations when
such payment of performance is due.

     8.   Pledgee's Rights upon Default.  Upon the occurrence of any default as
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defined in the preceding section, Pledgee may, if Pledgee so elects in its sole
option:

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          (a)  at any time and from time to time, sell, assign and deliver the
whole or any part of the Collateral at a sale through a broker in a public
market where securities of the type constituting such Collateral are usually
traded, without any advertisement, presentment, demand for performance, protest,
notice of protest, notice of dishonor or any other notice;

          (b)  at any time and from time to time sell, assign and deliver all or
any part of the Collateral, or any interest therein, at any other public or
private sale, for cash, on credit or for other property, for immediate or future
delivery without any assumption of credit risk, and for such price or prices and
on such terms as Pledgee in its absolute discretion may determine, provided that
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(i) at least ten days' notice of the time and place of any such sale shall be
given to Pledgor, and (ii) in the case of any private sale, such notice shall
also contain the terms of the proposed sale and Pledgee shall sell the
Collateral proposed to be sold to any purchaser procured by Pledgor who is
ready, willing and able to purchase, and who prior to the time of such sale
tenders the purchase price of, such Collateral on terms more favorable to
Pledgee than the terms contained in such notice;

          (c)  exercise the right to vote, the right to receive cash dividends
and other distributions, and all other rights with respect to the Collateral as
though Pledgee were the absolute owner thereof, whether or not such rights were
retained by Pledgor as against Pledgee before default; and

          (d)  exercise all other rights available to a secured party under the
Uniform Commercial Code and other applicable law.

     9.   Application of Sale Proceeds. In the event of a sale of Collateral,
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the proceeds shall first be applied to the payment of the expenses of the sale,
including brokers' commissions, counsel fees, any taxes or other charges imposed
by law upon the Collateral or the transfer thereof and all other charges paid or
incurred by Pledgee pertaining to the sale;

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and, second, to satisfy outstanding Obligations, in the order in which Pledgee
elects in its sole discretion; and, third, the surplus (if any) shall be paid to
Pledgor.

     10.  Notices. All notices made or required to be made hereunder shall be
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sent by United States first class or certified or registered mail, with postage
prepaid, or delivered by hand to Pledgee or to Pledgor at the addresses first
above written. Notice by mail shall be deemed to have been made on the date when
the notice is deposited in the mail.

     11.  Heirs, Successors, Etc. This Pledge Agreement and all of its terms and
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provisions shall benefit and bind the heirs, successors, assigns, transferees,
executors and administrators of each of the parties hereto. If this Pledge
Agreement is executed by more than one Pledgor, then (a) "Obligations" shall
include the Obligations of either or both of the Pledgors, (b) Pledgors shall be
in default if any of the events described in Section 7 above takes place with
respect to either Pledgor, (c) any notice required of Pledgee shall be given to
both Pledgors and (d) all Pledgors' covenants, warranties and representations
hereunder shall be joint and several.

     12.  Pledgee's Forbearance. Any forbearance, failure or delay by Pledgee in
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exercising any right, power or remedy hereunder shall not be deemed a waiver of
such right, power or remedy. Any single or partial exercise of any right, power
or remedy of Pledgee shall continue in full force and effect until such right,
power or remedy is specifically waived in writing by Pledgee.

     EXECUTED under seal at Boston, Massachusetts as of the date first above
written.

                              /s/ Doros Platika
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                              Doros Platika


                              ONTOGENY, INC.


                              By:__________________________________

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                                   EXHIBIT A
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               400,000 shares of Common Stock of Ontogeny, Inc.

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