Document:

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                                                                   Exhibit 10.15

                                                                  EXECUTION COPY

                       THIRD LEASE MODIFICATION AGREEMENT

                          Kenvic Associates, Landlord

                                      with

                          Instinet Corporation, Tenant

                                October 21, 1994
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                       THIRD LEASE MODIFICATION AGREEMENT

            THIS THIRD LEASE MODIFICATION AGREEMENT (the "Agreement"), dated as
of October 21, 1994, between KENVIC ASSOCIATES, a partnership having an office
at 875 Third Avenue, New York, New York 10022 ("Landlord") and INSTINET
CORPORATION, a Delaware corporation having an office at 875 Third Avenue, New
York, New York 10017 ("Tenant").

                              W I T N E S S E T H:

            WHEREAS, Landlord and Tenant are parties to that certain lease dated
as of November 19, 1992, as modified by a Lease Modification Agreement dated as
of July 9, 1993 (the "First Lease Modification Agreement") between Landlord and
Tenant, relating to the entire eighteenth (18th), twenty-eighth (28th) and
twenty-ninth (29th) floors in the Building and a Second Lease Modification
Agreement dated June 7, 1994 (the "Second Lease Modification Agreement") between
Landlord and Tenant relating to a portion of the twenty-seventh (27th) floor of
the Building (said lease, as so modified by the First Lease Modification
Agreement and the Second Lease Modification Agreement, is called the "Lease");
and
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            WHEREAS, Landlord and Tenant desire to modify the Lease on the terms
and conditions hereinafter set forth.

            NOW, THEREFORE, in consideration of the premises, and for good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, and for the mutual agreements herein, the Lease is amended as
follows:

            1. All the terms of the Lease, the initial letters of which are
capitalized and not otherwise defined, shall have the meanings set forth in the
Lease.

            2. Section 1.02 of the Lease is modified by adding to the Premises a
portion of the third (3rd) floor of the Building as indicated by the cross
hatching on Exhibit A annexed hereto (the "Additional 3rd Floor Premises"). The
rentable square foot area of the Additional 3rd Floor Premises is hereby deemed
to be 10,000 rentable square feet. As used in the Lease, the term "Premises"
shall include the Additional 3rd Floor Premises.

            3. Section 3.01 of the Lease is hereby modified so that the Fixed
Rent payable under the Lease is increased as follows:

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                  A. From and after August 1, 1995 until February 28, 1999, the
Fixed Rent shall be increased by $250,000 per annum; and

                  B. From and after March 1, 1999 through and including the
Expiration Date, the Fixed Rent shall be increased by an additional $20,000, per
annum.

            4. Articles 6 (TAX PAYMENTS) and 7 (ESCALATION) of the Lease are
hereby modified (and Paragraph 5 of the Second Lease Modification Agreement is
superseded) so that the Tenant's Share is increased to 16.61% (or, if reduced in
accordance with Section 6.01(a)(v), to 16.51%); provided however (A) for
purposes of Article 6, (a) the Base Tax for 12.9/16.61 of the Tenant's Share
shall be Real Estate Taxes for the 1993/1994 Tax Year and (b) the Base Tax for
3.74/16.61 of the Tenant's Share shall be Real Estate Taxes for the 1994/1995
Tax Year and (B) for purposes of Article 7, (a) the Expense Base for 12.9/16.61
of the Tenant's Share shall be the average of the Expenses for the 1993 Calendar
Year and the 1994 Calendar Year, (b) the Expense Base for 2.18/16.61 of the
Tenant's Share shall be the 1994 Calendar Year and (c) the Expense Base for
1.53/16.61 of the Tenant's Share shall be the 1995 Calendar Year.

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            5. Tenant has inspected the Additional 3rd Floor Premises and
acknowledges that the Additional 3rd Floor Premises is in good order and repair
and accepts the Additional 3rd Floor Premises for occupancy (including any
mechanical/electrical equipment, wherever located) in its present condition "AS
IS" on the date hereof, except as hereinafter provided, except that Landlord
shall (A) in accordance with Exhibit B annexed hereto, in lieu of performing any
work with respect to the Additional 3rd Floor Premises, except as set forth in
clause (B) of this paragraph 5, provide a Tenant's Work Allowance (as defined in
Exhibit B) of $100,000 and (B) prepare the demising wall indicated on Exhibit A
in a building standard manner for a first class office building at such time as
not to delay the performance by Tenant of its Finish Work (but in no event later
than the date Tenant completes its Finish Work) and at the sole cost and expense
of Landlord.

            6. The Lease is further modified as follows:

                  A. By adding to Section 10.10 of the lease "or the Additional
3rd Floor Premises" after the words "Additional 27th Floor Premises" on line 4
of said section.

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                  B. By modifying subparagraph D of paragraph 8 of the Second
Lease Modification Agreement (which modifies Section 16.02 of the Lease) by
inserting in clause (ii) of said Section (i) after the words "nineteen (19th)
floor" on line 13 of said subparagraph, the following: ", the Additional 3rd
Floor Premises" and (ii) after the words "19th Floor, on line 20, the words "on
the first day of the term of the lease of the Additional 3rd Floor Premises,
with respect to the 3rd Floor,".

                  C. By deleting from the last sentence of Section 22.09 of the
Lease the number "100,500" and replacing it with the number "110,875".

                  D. By inserting in Section 24.02 of the Lease (i) after the
word "ducts" on line 2 thereof the words ", with respect to the Additional 3rd
Floor Premises, louvered vents, supplemental HVAC equipment" and (ii) after the
word "walls" on line 3 thereof, the word "windows".

                  E. By modifying Section 24.03 of the Lease to add the
following sentence: "Tenant acknowledges that exterior louvered vents, condenser
units, refrigerant piping and electrical power connections for a supplemental
air conditioning system having a capacity of approximately 7.5

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tons, for a tenant of an adjacent portion of the third (3rd) floor of the
Building is or will be located in ceiling plenum space in the Additional 3rd
Floor Premises. Tenant agrees that the tenant of such adjacent premises, and its
contractors and workers, may, from time to time, have access to the Additional
Third Floor Premises, as an agent of Landlord acting under this Section 24.03
for the purpose of installing, maintaining, servicing and replacing said
equipment; provided, however, the tenant of such adjacent premises shall perform
its work to install the louvered vents, condenser units, refrigerant piping and
electrical power at such times as shall not delay the performance by Tenant of
its Finish Work (but in no event later than the date Tenant completes its Finish
Work)."

                  F. By modifying Section 43.01 of the Lease by inserting on
line 26 thereof, after the word "including," the words "the Additional 3rd Floor
Premises".

                  G. By modifying Section 46.01 of the Lease by deleting the
word "or" in line 22 thereof.

                  H. By modifying Section 46.02 of the Lease by deleting the
period on line 12 thereof and adding after

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the word "floors" on lines 8 and 12 the following: "as of the first day of the
Expansion Term".

      7. There is hereby added to the Lease a new Article 44 of the Lease to
read as follows:

                                   ARTICLE 44

                          Third Floor Expansion Option

            Section 44.01. If, during the Term of the Lease, Tenant is not in
default under the Lease beyond any applicable notice and grace period, and
provided (A) Tenant, and all related corporations (as defined in Section 22.03
of the Lease), which are a permitted sublessee or sub-sublessee of the Premises
and have continuously qualified as a related corporation, have not subleased, in
the aggregate, more than forty percent (40%) of the entire Premises to one or
more corporations or other business entities which are not related corporations,
and the remaining sixty percent (60%) of the Premises is in the possession of
Tenant or a related corporation, (B) Tenant gives notice (the "Third (3rd) Floor
Expansion Election Notice") to Landlord within thirty (30) days (with respect to
which Third (3rd) Floor Expansion Election Notice time is expressly of the
essence) after Landlord has sent to Tenant a notice (the "Landlord Third (3rd)
Floor Expansion Space Availability Notice") setting

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forth the date on which Landlord reasonably expects to tender Vacant Possession
of a portion of the Third (3rd) Floor of the Building now occupied by the
Landlord and its subtenants, occupants and Affiliates of Landlord (hereinafter
defined) as indicated by the cross-hatching on Exhibit C annexed hereto
("Landlord's Occupied Space"), (C) if a Landlord Third (3rd) Floor Expansion
Space Availability Notice is sent after the earliest date on which a First
Renewal Term Election Notice may be sent by Tenant, Tenant has theretofore
exercised its Extension Option pursuant to a First Renewal Term Election Notice
(or a Conditional First Renewal Term Election Notice with respect to which the
Renewal Condition was withdrawn or deemed withdrawn) in accordance with Article
43 (EXTENSION OPTION) and (D) Tenant complies with the conditions set forth
below, Tenant shall have the one-time option (the "Third (3rd) Floor Expansion
Option") to lease the Landlord's Occupied Space for a term commencing on the
date Vacant Possession of the Landlord's Occupied Space is tendered to Tenant
and ending on the last day of the Term of the Lease (the "Third (3rd) Floor
Expansion Term"), upon the same terms and conditions set forth in the Lease
(unless changed or modified by this Agreement or other mutual agreement).
Landlord shall send a Landlord Third (3rd) Floor Expansion Availability Notice
at such time as it reasonably believes it knows the date on

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which it reasonably expects to deliver Vacant Possession of the Landlord's
Occupied Space. As used in this Agreement the term "Affiliates" shall mean any
(a) firm, corporation or partnership, limited or general, of which (x) a
principal of Landlord or (y) any partner of (i) Landlord or (ii) any principal
of Landlord or (z) any spouse, issue or sibling or trust for the benefit of any
spouse, issue, sibling of such principal or partner, is either an officer,
director, shareholder or other equity owner or (b) spouse, issue or sibling of
any principal of Landlord, partner of Landlord or of any such principal or trust
for the benefit of any such spouse, issue or sibling. Landlord and Tenant each
acknowledge that Landlord need not give a Landlord Third (3rd) Floor Expansion
Space Availability Notice after July 31, 2003, whether or not Vacant Possession
of the Landlord's Occupied Space is thereafter obtained by Landlord. The
Landlord and Tenant agree that rentable square feet of the Landlord's Occupied
Space is 5,000. Vacant Possession of such Landlord's Occupied Space will be
tendered to Tenant on the date, if at all, on which Vacant Possession thereof is
obtained by Landlord, at the Fixed Rent and Additional Rent provided below.
Notwithstanding the foregoing, Tenant may not exercise the Third (3rd) Floor
Expansion Option for the Landlord's Occupied Space unless all of the following
additional conditions X, Y and Z are met:

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                  X. The Third (3rd) Floor Expansion Election Notice states that
Tenant elects to add to the Premises all of the Landlord's Occupied Space; and

                  Y. No Third (3rd) Floor Expansion Election Notice may be sent
by Tenant under this Article after the sending of an Expansion Election Notice
under Section 46.01 and prior to the first day of the Expansion Term, unless at
the time of sending the Third (3rd) Floor Expansion Election Notice and on the
first day of the Expansion Term (1) the most recent audited financial statement
of Tenant and each of the FOCUS Reports filed with the SEC during the twelve
(12) months prior to such first day shows a net worth of not less than $185
million and a Net Capital of not less than $56 million and (2) the Third (3rd)
Floor Expansion Election Notice is accompanied by such financial statement and
FOCUS Reports; and

                  Z. Tenant shall not be in default under any of the terms,
covenants and conditions of the Lease beyond any notice and grace period
hereunder at the time it sends the Third (3rd) Floor Expansion Election Notice.

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            Section 44.02. In the event that Tenant validly exercises the Third
(3rd) Floor Expansion Option for the Landlord's Occupied Space:

            The Fixed Rent per rentable square foot with respect to the
Landlord's Occupied Space, payment of which shall commence on the first day of
the Third (3rd) Floor Expansion Term, shall be an amount equal to aggregate of
(A) the Fixed Rent per rentable square feet for the 18th floor as of the first
day of the Third (3rd) Floor Expansion Term and (B) the Additional Rent for Tax
Escalation under Article 6 (Tax Payments) and for Expense Escalation under
Article 7 (ESCALATION) per rentable square foot for the 18th floor as of the
first day of the Third (3rd) Floor Expansion Term. In addition, if the Third
(3rd) Floor Expansion Term commences prior to August 1, 1998, on August 1, 1998
Fixed Rent shall be increased by $20,000 PER ANNUM. With respect to such
Landlord's Occupied Space, the Base Tax under Article 6 (TAX PAYMENTS) shall be
the Real Estate Taxes for the Tax Year in which any portion of the Third (3rd)
Floor Expansion Term shall fall and the Expense Base under Article 7
(ESCALATION) shall be the calendar year of commencement of the Third (3rd) Floor
Expansion Term. The Tenants Share, as used in said Articles 6 (TAX PAYMENTS) and
7 (ESCALATION) shall be increased based upon the number of rentable square

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feet of the Landlord's Occupied Space. The Third (3rd) Floor Expansion Term
shall commence on the date of the tender to Tenant of Vacant Possession of the
Landlord's Occupied Space.

            Section 44.03. In the event Tenant validly exercises the Third (3rd)
Floor Expansion Option under this Article, the parties shall immediately be
bound thereby without the execution of an amendment to this Lease; however, at
the request of either party, the parties shall promptly execute and deliver a
written amendment to this Lease reflecting the addition of such Landlord's
Occupied Space as part of the Premises for the Third (3rd) Floor Expansion Term,
the increase of the Fixed Rent and the increase of the Tenant's Share as
provided above by reason of the addition of such Landlord's Occupied Space.
Except for such changes, the provisions of this Lease shall apply with respect
to such Landlord's Occupied Space and such Landlord's Occupied Space shall be
and become part of the Premises. Tenant will accept possession of such
Landlord's Occupied Space, and the facilities thereto and improvements therein
in the then "AS IS" condition on the date of delivery thereof to Tenant and,
Landlord shall not be required to perform any work or to give Tenant any work
allowance whatsoever with respect to any such Landlord's

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Occupied Space except that the Landlord's Occupied Space will be delivered broom
clean, and free of asbestos and Landlord shall, after receipt of a complete set
of fully dimensioned and specified mechanical/electrical drawings for such
Landlord's Occupied Space, prepare the demising wall indicated on Exhibit C in a
building standard manner for a first class office building at such time as not
to delay performance by Tenant of any Finish Work therein (but in no event later
than the date Tenant completes its Finish Work) and at the sole cost and expense
of Landlord. Notwithstanding the foregoing, in the event Landlord fails or is
unable to tender Vacant Possession of all or any portion of such Landlord's
Occupied Space to Tenant on the proposed delivery date thereof as a result of
Force Majeure, the performance by Landlord of Removal Work or, after the sending
of a Tenant's Third (3rd) Floor Expansion Notice, the holding over of any
subtenant, occupant or Affiliate of Landlord, or otherwise, Landlord shall not
be subject to any liability whatsoever for such failure or inability to tender
Vacant Possession during the continuation of the Force Majeure, such holding
over by such subtenant, occupant or Affiliate or the performance of such Removal
Work, or otherwise, but the Fixed Rent and Additional Rent shall not commence
with respect to such portion of such Landlord's Occupied Space until the date on
which Vacant Possession

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thereof is actually tendered to Tenant; provided, however, (A) that if the
failure to deliver Vacant Possession in accordance with the foregoing provision
is due solely to the holding over of a subtenant, occupant or Affiliate of
Landlord, Landlord shall thereafter promptly commence an action to obtain Vacant
Possession of Landlord's Occupied Space and diligently prosecute such action to
completion, and (B) if Landlord fails to fulfill its obligations under clause
(A) and is so notified by Tenant and fails to cure such failure within ten (10)
days after such notice from Tenant, Tenant may, at its own cost and expense,
commence and prosecute such action. Notwithstanding the foregoing, if Vacant
Possession of any Landlord's Occupied Space is not tendered by Landlord within
twelve (12) months following the date set forth in the Landlord's Occupied Space
Availability Notice, Tenant may, by notice given to Landlord after such twelve
(12) month period has expired but prior to the date Vacant Possession is
tendered to Tenant, elect to cancel its Third (3rd) Floor Expansion Election
Notice but only with respect to such Landlord's Occupied Space as to which such
Vacant Possession has not been tendered. For purposes of computing the twelve
(12) month period referred to above, the Removal Period shall not be included in
such computation. Nothing herein shall operate to extend the Expiration Date for
any of the

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Premises (including but not limited to such Landlord's Occupied Space) beyond
the date otherwise fixed for the expiration of the Term or of the Expansion
Term, as applicable.

            Section 44.04. Time shall be expressly of the essence with respect
to all notices given by Tenant under this Article, and the time periods for the
giving of such notices shall not be extended for any reason whatsoever.

            Section 44.05. In the event Tenant shall fail to send to Landlord a
Third (3rd) Floor Expansion Election Notice in response to a Landlord Third
(3rd) Floor Expansion Space Availability Notice within the applicable time
period as provided herein, Tenant shall be conclusively deemed to have failed to
have exercised its Third (3rd) Floor Expansion Option with respect to such
Landlord Third (3rd) Floor Expansion Space Availability Notice, and Tenant
agrees that no action taken subsequently by Landlord or by Tenant shall operate
to revive any rights of Tenant under this Article with respect to the Landlord's
Occupied Space.

            Section 44.06. A. The rights of Tenant under this Article, except
for those rights of Tenant set forth in Section 44.08, are subject to the rights
of the Landlord,

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and of any and all present and future direct or indirect subtenants, occupants
and Affiliates of Landlord with respect to (1) the existing lease with respect
to the Landlord's Occupied Space, as the same may be amended or modified from
time to time after the date hereof by Landlord and the tenant under such lease
(such lease, as it may be so amended or modified is called the "Landlord's Space
Lease") and (2) the Landlord's Occupied Space. Except for the provisions of
Section 44.08, nothing contained in this Agreement or the sending to Tenant of
any Landlord Third (3rd) Floor Expansion Space Availability Notice or the
sending by Tenant of a Third (3rd) Floor Expansion Election Notice in response
to a Landlord Third (3rd) Floor Expansion Space Availability Notice shall be
construed (1) to grant any rights to Tenant with respect to any Landlord's
Occupied Space prior to such space being expressly included in any Landlord
Third (3rd) Floor Expansion Space Availability Notice, Tenant expressly
acknowledging that Landlord is under no duty to cause the tenant under the
Landlord's Space Lease to waive its rights thereunder or to deliver Vacant
Possession of all or any part of Landlord's Occupied Space and that Landlord may
never be able to send a Landlord Third (3rd) Floor Expansion Space Availability
Notice with respect thereto and that Landlord may, if it so elects in its sole
discretion, actively deal in any manner with the tenant

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under the Landlord's Space Lease in such a manner as may prevent such tenant
from surrendering or waiving (or in such manner as may induce such tenant not
ever to surrender or waive) all of its rights to the Landlord's Occupied Space,
(2) to prevent Landlord from negotiating with the tenant under the Landlord's
Space Lease or from entering into one or more modifications of the Landlord's
Space Lease, which modification or modifications may contain modifications to
the rental or other provisions thereof or grant renewal or extension options in
favor of the tenant under the Landlord's Space Lease, the term of which may
extend past the Term of this Lease as it may be extended, (3) to obligate
Landlord to (a) refuse its consent to any proposed sublease or assignment by the
tenant under the Landlord's Space Lease of all or any portion of the Landlord's
Occupied Space, (b) accept a surrender by the tenant of the Landlord's Space
Lease of its rights with respect to the Landlord's Occupied Space or (c) agree
with the tenant under the Landlord's Space Lease to cancel or modify the rights
of such tenant with respect to such Landlord's Occupied Space, (4) to obligate
Landlord to evict the tenant under the Landlord's Space Lease if in default
thereunder, or (5) to obligate Landlord to vacate the Landlord's Occupied Space
or cause any present or future direct or indirect Affiliate or subtenant or
occupant in possession of any portion thereof

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to vacate all or any Landlord Occupied Space, even if the effect of any such
action or inaction described in clauses (1) to (5) inclusive considered singly
or cumulatively, may be to preclude Vacant Possession of any Landlord's Occupied
Space from ever occurring or otherwise materially and adversely affect the
possibility of tendering of Vacant Possession of the Landlord's Occupied Space
to Tenant;

            B. Except for the provisions of Section 44.08, anything herein
contained to the contrary notwithstanding, Tenant's expansion option with
respect to the Landlord's Occupied Space is conditioned upon and is subject and
subordinate to (1) the provisions of paragraph A of this Section and (2) the
tenant under the Landlord's Space Lease surrendering to Landlord or waiving all
of its rights to the Landlord's Occupied Space. Tenant hereby acknowledges that
except as set forth in Section 44.08, it has no right under this Article 44 or
any other provision of this Agreement or the Lease with respect to the
Landlord's Occupied Space unless and until the tenant under the Landlord's Space
Lease so surrenders or waives such rights. Promptly after Landlord and the
tenant under the Landlord's Space Lease unconditionally and irrevocably agree to
the waiver by such tenant or its surrender to Landlord of all of its rights to
the Landlord's Occupied Space, Landlord will notify Tenant

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thereof pursuant to a Landlord Third (3rd) Floor Availability Notice; provided,
however, Landlord shall not be required to give Tenant a Landlord Third (3rd)
Floor Availability Notice after July 31, 2003.

            Section 44.07. In addition to the limitation of liability set forth
in Section 44.03, Tenant expressly waives any right to rescind this Lease under
Section 223-a of the New York Real Property Law or under any present or future
statute of similar import then in force and further expressly waives the right
to recover any damages, direct or indirect, which may result from Landlord's
failure to deliver Vacant Possession of the Landlord's Occupied Space on the
commencement date of the Third (3rd) Floor Expansion Term. Tenant agrees that
the provisions of this Article are intended to constitute "an express provision
to the contrary" within the meaning of said Section 223-a. Any such failure to
so deliver Vacant Possession shall not extend the expiration date of the Third
(3rd) Floor Expansion Term. Notwithstanding the foregoing provisions of this
Section 44.07, in the event that the failure to deliver Vacant Possession of any
Landlord's Occupied Space on the commencement date of the Third (3rd) Floor
Expansion Term is not the result of Force Majeure, the holding over of the prior
tenant or the performance of Removal Work, Tenant may,

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not earlier than sixty (60) days after the commencement date of the First
Renewal Term, elect to cancel its Third (3rd) Floor Expansion Election Notice
with respect to such Landlord's Occupied Space. For purposes of computing the
sixty (60) day period referred to above, the Removal Period shall not be
included in such computation.

            Section 44.08. At any time prior to the sending to Tenant of a
Landlord Third (3rd) Floor Expansion Space Availability Notice, Tenant may, on
one occasion, send Landlord a notice (the "Tenant's Third (3rd) Floor Expansion
Notice") that it elects to expand the Premises to include the Landlord's
Occupied Space, provided however, no Tenant's Third (3rd) Floor Expansion Notice
may be sent unless Tenant is on the date of the sending of such Tenant's Third
(3rd) Floor Expansion Notice in compliance with all of the conditions set forth
in Section 44.01 which are required to be complied with to enable Tenant to give
a Third (3rd) Floor Expansion Election Notice. Upon the giving by Tenant of a
valid Tenant's Third (3rd) Floor Expansion Notice, Tenant shall be deemed to
have sent a timely Third (3rd) Floor Expansion Election Notice and to have
validly exercised the Third (3rd) Floor Expansion Option for which purposes the
provisions of Sections 44.01 to 44.03 inclusive and 44.07 shall apply, except
that Landlord need not deliver

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Vacant Possession of the Landlord's Occupied Space prior to one (1) year after
having received the Tenant's Third (3rd) Floor Expansion Notice. In the event of
any failure of Landlord to deliver Vacant Possession of Landlord's Occupied
Space, within one (1) year after having received Tenant's Third (3rd) Floor
Expansion Notice, Tenant's sole remedies by reason of such failure shall be
either to (A) rescind Tenant's Third (3rd) Floor Expansion Notice or (B) sue for
specific enforcement of Landlord's covenant to deliver such Vacant Possession,
but in no event may Tenant assert any claim against Landlord or any Affiliates
of Landlord for damages by reason of such failure.

            8. Landlord represents, warrants and covenants that:

                  A. The Building Equipment which serves the Additional 3rd
Floor Premises shall be in working order on the date Vacant Possession of the
Additional 3rd Floor Premises shall be delivered to Tenant.

                  B. No asbestos was used in the construction of the Additional
3rd Floor Premises by Landlord. Landlord has no actual knowledge (as
distinguished from imputed or implied knowledge) that any Hazardous Substance
(as so

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designated on the date of execution of the Second Lease Modification
Agreement) was used in the construction of the Additional 3rd Floor Premises. In
the event any Hazardous Substance (as so designated as of the date of execution
of the Second Lease Modification Agreement) or asbestos is found in the
Additional 3rd Floor Premises, Landlord shall be deemed to have made the
Reimbursement Election.

                  C. (1) Tenant shall have access, upon prior reasonable notice,
to the electrical closets on the third floor of the Building which services the
third floor of the Building for installation of Tenant's initial electrical
equipment and/or for repair and maintenance thereof and, in connection with such
installation, to permit it to tap into the electrical riser and to upgrade the
existing electrical service provided to the third floor of the Building.
Provided that (A) there shall be made available to the new tenant of the
adjacent premises 70 amps of 4-wire, 460 volt, 3-phase separately metered
electrical power (the cost of installation of which shall be borne by the tenant
of the adjacent premises) and (B) the existing electrical service to the
premises now occupied by Landlord, including Landlord's Occupied Space shall be
maintained, all remaining existing electrical power now serving the third floor
of the Building may be used by Tenant. All of the

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foregoing work shall be performed by Coyne Electrical Contractors, Inc. which
shall be retained by Tenant at its sole cost and expense to perform such work.
Landlord makes no representation that the electrical power being made available
to Tenant is adequate for Tenant's needs.

                        (2) Landlord hereby grants Tenant the right to construct
and install a 200 amp, 460 volt, 3-phase electrical switch in a location in the
Building's frame room approved by Landlord in Landlord's sole discretion and to
erect a riser to provide electrical service to the Additional 3rd Floor
Premises. All aspects of the design and construction of the new switch and riser
shall be subject to the Landlord's right of approval which shall not be
unreasonably withheld or delayed and shall be further subject to the
unconditional approval of (1) Consolidated Edison, (2) Landlord's engineer and
(3) Tenant's engineer. In addition, Tenant must comply with all Legal
Requirements and any power shut-downs and the performance of this work must be
accomplished "off hours" and must not interfere with the business of any other
tenant in the Building. All costs associated with the foregoing work shall be
paid for by Tenant, including the cost of Landlord's engineer.

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            9. Landlord shall make available to Tenant freight elevator service
subject to the following conditions:

                  A. If Tenant desires to use the freight elevator only (i)
between the Additional (3rd) Floor Premises and the truck dock, (ii) on two (2)
occasions between 4 PM and 8 PM on each Business Day and (iii) to enable
overnight courier services to pick up packages, Tenant shall give Landlord at
least twenty-four (24) hours prior written notice requesting the use of the
freight elevator for such purposes, which notice may request such use for no
more than two (2) consecutive hours during any twenty-four (24) hour period.

                  B. Landlord may refuse to honor any request by Tenant pursuant
to subparagraph A to use the freight elevator if the request by Tenant conflicts
with Landlord's then applicable Rules and Regulations, prior reservations from
other tenants of the Building, Landlord's own needs or anticipated needs, or any
emergency requirements for the use of freight elevator, provided however, in
such event, Tenant may use a passenger elevator.

                                      -24-
<PAGE>   26

                  C. Landlord shall not charge Tenant for using the freight
elevator in accordance with and subject to the provisions of subparagraph A
except for those hours of freight elevator usage which Tenant reserves in excess
of two hundred fifty (250) aggregate hours during each calendar year, PRO RATED
for the first and last year of the Term and, with respect to such excess usage,
Tenant shall pay Landlord its then prevailing charges for such elevator usage,
which charges shall be deemed Additional Rent.

            10. Tenant represents that in the negotiation of this Agreement it
dealt with no broker(s) other than The Peregrine White Company, Inc. (the
"Broker") and no other broker participated in bringing about this Agreement.
Tenant hereby indemnifies and agrees to defend and hold Landlord harmless
against any claim or liability arising out of any inaccuracy or alleged
inaccuracy of the above representation. The parties hereto acknowledge that the
Broker will be paid a commission in accordance with a separate agreement between
Landlord and Broker. Landlord represents that to the best of Landlord's
knowledge, it has not dealt with any broker other than the Broker in connection
with this Agreement.

                                      -25-
<PAGE>   27

            11. Except as modified by this Agreement, the Lease shall remain in
full force and effect in accordance with its terms and (except for the
representations set forth therein) is hereby ratified and confirmed.

            12. This Agreement shall be binding on and shall inure to the
benefit of the parties hereto and their respective successors and permitted
assigns.

            IN WITNESS WHEREOF, the parties have caused this Agreement to be
executed as of the date first above written.

                                        LANDLORD:

                                        KENVIC ASSOCIATES

WITNESS:

/s/ John C. Lisher                      By: /s/ Lucille Gladstone
----------------------------------          ------------------------------------
                                            Name:  Lucille Gladstone
                                            Title: Partner

                                        TENANT:

                                        INSTINET CORPORATION

WITNESS:

/s/ Steven R. Goodman                   By: /s/ Mark Nienstedt
----------------------------------          ------------------------------------
                                            Name:  Mark Nienstedt
                                            Title: Senior Vice President

                                      -26-
<PAGE>   28

                           LANDLORD'S ACKNOWLEDGEMENT

STATE OF NEW YORK       )
                        : ss.:
COUNTY OF NEW YORK      )

            On this 21st day of October, 1994, before me personally came Lucille
Gladstone, to me known, who, being by me duly sworn, did depose and say that she
is a partner in the firm of KENVIC ASSOCIATES, a New York partnership, and that
she executed the foregoing instrument as and on behalf of said partnership.

                                        /s/ Elizabeth Diaks
                                        ----------------------------------------
                                        Notary Public

                                                        ELIZABETH DIAKS
                                                Notary Public, State of New York
                                                        No. 01BU4987648
                                                   Qualified in Nassau County
                                                  Commission Expires 10/21/95

                      CORPORATE TENANT'S ACKNOWLEDGEMENT

STATE OF NEW YORK       )
                        : ss.:
COUNTY OF NEW YORK      )

            On this 21st day of October, 1994, before me personally came Mark
Nienstedt, to me known, who, being by me duly sworn, did depose and say that he
resides at One Capoolong Creek Lane, Pittstown, New Jersey 08867; that he is the
Executive Vice President of Instinet Corporation, the corporation described in
and which executed the foregoing Lease, as Tenant, and that he signed his name
thereto by order of that corporations' board of directors.

                                        /s/ Howard Brown
                                        ----------------------------------------
                                        Notary Public

           HOWARD BROWN
 Notary Public, State of New York
         No. 01BR5024906
   Qualified in New York County
Commission Expires March 21, 1996

                                      -27-<PAGE>   1
                                                                   Exhibit 10.16

                                                                  EXECUTION COPY

                      FOURTH LEASE MODIFICATION AGREEMENT

                          Kenvic Associates, Landlord

                                      with

                          Instinet Corporation, Tenant

                               February 14, 1996

<PAGE>   2

                      FOURTH LEASE MODIFICATION AGREEMENT

      THIS FOURTH LEASE MODIFICATION AGREEMENT (the "Agreement"), dated as of
February 14, 1996, between KENVIC ASSOCIATES, a partnership having an office at
875 Third Avenue, New York, New York 10022 ("Landlord") and INSTINET
CORPORATION, a Delaware corporation having an office at 875 Third Avenue, New
York, New York 10022 ("Tenant").

                              W I T N E S S E T H:

      WHEREAS, Landlord and Tenant are parties to that certain lease dated as of
November 19, 1992, as modified by a Lease Modification Agreement dated as of
July 9, 1993 (the "First Lease Modification Agreement") between Landlord and
Tenant, relating to the entire eighteenth (18th), twenty-eighth (28th) and
twenty-ninth (29th) floors in the Building; a Second Lease Modification
Agreement dated June 7, 1994 (the "Second lease Modification Agreement") between
Landlord and Tenant relating to a portion of the twenty-seventh (27th) floor of
the Building and a Third Lease Modification Agreement dated as of October 21,
1994 (the "Third Lease Modification Agreement") between Landlord and Tenant,
relating to a portion of the third (3rd) floor in the Building (said lease, as
so modified by the First Lease Modification Agreement, the Second Lease
Modification

<PAGE>   3

Agreement and the Third Lease Modification Agreement, is hereinafter referred to
as, the "Lease");

      WHEREAS, pursuant to the Second Lease Modification Agreement, Tenant has
exercised its option to Lease the entire nineteenth (19th) floor of the Building
(the "Additional 19th Floor Premises").

      WHEREAS, Landlord and Tenant desire to modify the Lease as hereinafter set
forth;

      NOW, THEREFORE, in consideration of the premises, and for good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, and of the mutual agreements herein, the Lease is amended as
follows:

      1. All the terms of this Agreement, the initial letters of which are
capitalized and not otherwise defined, shall have the meanings set forth in the
Lease.

      2. Effective upon the delivery of Vacant Possession of the Additional 19th
Floor Premises (the "19th Floor Delivery Date"), Section 1.02 of the Lease is
modified by adding to the Premises the Additional 19th Floor Premises and the
term "Premises" shall thereafter include the Additional 19th Floor Premises. The
rentable square foot area of the Additional 19th Floor Premises is hereby deemed
to be 26,000 rentable square feet.

                                      -2-

<PAGE>   4

      3. Sections 7C(a) of the First Lease Modification Agreement is hereby
deleted in its entirety and replaced with the following:

      "(a) Tenant acknowledges that the existing tenant of the Additional 19th
      Floor Premises has consented to the entry of a judgment of possession of
      the Additional 19th Floor Premises and to the issuance of a warrant of
      eviction granting legal and physical possession of the Additional 19th
      Floor Premises to Landlord but with a stay of the execution of such
      warrant of eviction until no later than November 30, 1996. Commencing no
      later than December 2, 1996, Landlord will use all reasonable efforts to
      cause the warrant of eviction to be executed. No later than one (1)
      business day after the date legal and physical possession is delivered to
      Landlord upon the execution of such warrant of eviction, Landlord shall
      deliver a written notice to Tenant advising Tenant of such delivery.
      Tenant shall, within one (1) business day after such written notice is
      delivered, inspect the Additional 19th Floor Premises to determine if said
      Additional 19th Floor Premises are, in fact, free of all property of the
      former occupants thereof. Unless within said same business day on which
      the Tenant has such right to inspect, Tenant delivers a written notice to
      Landlord identifying property of the former occupant which remains on the
      Additional 19th Floor Premises, Landlord and Tenant agree that Vacant
      Possession of the Additional 19th Floor Premises shall be deemed to have
      been delivered by Landlord to Tenant one (1) business day after such
      written notice was delivered by Landlord to Tenant."

      4. Notwithstanding the provisions of Section 7(C) (a) of the First Lease
Modification Agreement, as modified by this Agreement, Landlord shall, at any
time after the date hereof that Vacant Possession of the Additional 19th Floor
Premises is delivered to Landlord (and

                                       -3-

<PAGE>   5

upon three (3) business days written notice to Tenant), deliver Vacant
Possession of the Additional 19th Floor Premises to Tenant, which delivery shall
be deemed to occur upon the expiration of said third (3rd) business day.

      5. Section 7E of the First Lease Modification Agreement is hereby modified
by (a) deleting the words "within five (5) months following the expiration of
the Kasowitz Lease" in the 23rd and 24th lines of said Section and replacing
them with the words "by February 15, 1997." and (b) deleting the words "9 months
after the expiration of the Kasowitz Lease" in line 27 of said Section and
replacing such words with the words "between February 16, 1997 and March 1,
1997".

      6. Section 7B(i) of the Second Lease Modification Agreement is hereby
modified by deleting said section and replacing it with the following:

            (i) By deleting subparagraph (b) from paragraph C of Section 7
      thereof and replacing it with the following:

            "(b) From and after the date of delivery or deemed delivery to
            Tenant of Vacant Possession of the Additional 19th Floor Premises,
            Fixed Rent, as defined in Article 3 of the Lease, shall be increased
            (i) if such Vacant Possession is delivered or deemed delivered prior
            to July 1, 1996, by $668,750 per annum for the period beginning on
            the date such Vacant Possession is delivered or deemed delivered and
            ending June 30,

                                      -4-

<PAGE>   6

            1996 and by an additional $43,650 per annum for the period from July
            1, 1996 through July 31, 1998 and (ii) if Vacant Possession is not
            delivered or deemed delivered prior to July 1, 1996 by $712,400 per
            annum for the period from the date on which such Vacant Possession
            is delivered or is deemed delivered through July 31, 1998. In
            addition, Fixed Rent shall be increased by an additional $104,000
            per annum from and after August 1, 1998."

      7. Effective as of the 19th Floor Delivery Date, Articles 6 (TAX PAYMENTS)
and 7 (ESCALATION) of the Lease are modified (and Paragraph 4 of the Third Lease
Modification Agreement and Subparagraph (c) of Paragraph (C) of Section 7 of the
First Lease Modification Agreement are superseded) so that the Tenant's Share is
increased to 19.96%; provided however (A) for purposes of Article 6, (a) the
Base Tax for 16.33/19.96 of the Tenant's Share shall be Real Estate Taxes for
the 1993/1994 Tax year, and (b) the Base Tax for 3.63/19.96 of the Tenant's
Share shall be Real Estate Taxes for the 1994/1995 Tax Year and (B) for purposes
of Article 7, (a) the Expense Base for 16.33/19.96 of the Tenant's Share shall
be the average of the Expenses for the 1993 Calendar Year and the 1994 Calendar
Year, (b) the Expense Base for 2.12/19.96 of the Tenant's Share shall be the
1994 Calendar Year and (c) the Expense Base for 1.51/19.96 of the Tenant's Share
shall be the 1995 Calendar Year. Tenant acknowledges that it is not entitled to
any

                                      -5-

<PAGE>   7

further reduction of Tenant's Share pursuant to the "provided, however" clause
at line 2 of Section 6.01(a) (v) of the Lease.

      8. Effective as of the 19th Floor Delivery Date, the Lease is further
modified as follows:

            A. By adding to Section 10.10 of the lease "or the Additional 19th
Floor Premises" after the words "Additional 3rd Floor Premises" on line 4 of
said section.

            B. By deleting from the last sentence of Section 22.09 of the Lease
the (i) words "execution and delivery of this Agreement" and replacing such
words with the words "19th Floor Delivery Date" and (ii) the number "110,875"
and replacing it with the number "136,875".

            C. by inserting in Section 24.02 of the Lease after the words "the
Additional 3rd Floor Premises" on line 2 thereof the words "and the Additional
19th Floor Premises."

            D. By modifying Section 43.01 of the Lease by inserting on line 26
thereof, after the word "including" the words "the Additional 19th Floor
Premises."

      9. Tenant represents that in the negotiation of this Agreement it dealt
with no broker other than Koll Management Services, Inc. (the "Broker") and no
other broker participated in bringing about this Agreement. Tenant hereby
indemnifies and agrees to defend and hold Landlord

                                      -6-

<PAGE>   8

harmless against any claim or liability arising out of any inaccuracy or alleged
inaccuracy of the above representation. The parties hereto acknowledge that the
Broker will be paid a commission in accordance with a separate agreement between
Landlord and Broker. Landlord represents that to the best of Landlord's
knowledge, it has not dealt with any broker other than the Broker in connection
with this Agreement.

      10. Except as modified by this Agreement, the Lease shall remain in full
force and effect in accordance with its terms and (except for the
representations set forth therein) is hereby ratified and confirmed.

      11. This Agreement shall be binding on and shall inure to the benefit of
the parties hereto and their respective successors and permitted assigns.

      IN WITNESS WHEREOF, the parties have caused this Agreement to be executed
as of the date first above written

                                    LANDLORD:

WITNESS:                            KENVIC ASSOCIATES

/s/ John C. Lisher                  By: /s/ Lucille Gladstone
----------------------------            -------------------------------
                                        Name: Lucille Gladstone
                                        Title: Partner

                                    TENANT:

WITNESS:                            INSTINET CORPORATION

                                    By: /s/ Daniel M. Rosenthal
----------------------------            -------------------------------
                                        Name: Daniel Rosenthal
                                        Title: Senior Vice President

                                      -7-

<PAGE>   9

                          LANDLORD'S ACKNOWLEDGEMENT

STATE OF NEW YORK  )
                   : ss.:
COUNTY OF NEW YORK )

            On this ___ day of February, 1996, before me personally came Lucille
Gladstone, to me known, who, being by me duly sworn, did depose and say that she
is a partner in the firm of KENVIC ASSOCIATES, a New York partnership, and that
she executed the foregoing instrument as and on behalf of said partnership.

                                                     ---------------------------
                                                            Notary Public

                       CORPORATE TENANT'S ACKNOWLEDGEMENT

STATE OF NEW YORK  )
                   : ss.:
COUNTY OF NEW YORK )

            On this 14th day of February, 1996, before me personally came Daniel
Rosenthal, to me known, who, being by me duly sworn, did depose and say that the
resides at
                                                                              ;
that he is the Senior Vice President of Instinet Corporation, the corporation
described in and which executed the foregoing Lease, as Tenant, and that he
signed his name thereto by order of that corporation's board of directors.

                                                     ---------------------------
                                                            Notary Public

                                      -8-

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