JOINT FILING AGREEMENT In accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, the undersigned hereby agrees to the joint filing with each other of the attached statement on Schedule 13G and to all amendments to such...

                                                                 
                                                                       





                             JOINT FILING AGREEMENT

         In accordance with Rule 13d-1(k)(1)  under the Securities  Exchange Act
of 1934, as amended, the undersigned hereby agrees to the joint filing with each
other of the attached  statement on Schedule 13G and to all  amendments  to such
statement and that such  statement and all  amendments to such statement is made
on behalf of each of them.

         IN WITNESS  WHEREOF,  the undersigned  hereby execute this agreement on
February 11, 1999.


                         /s/ Xxxx X. Xxxxx
                         -------------------------------------- 
                         Xxxx X. Xxxxx


                          VULCAN VENTURES INCORPORATED



                           By:  /s/ Xxxxxxx X. Xxxxx
                                --------------------------------
                                Xxxxxxx X. Xxxxx, Vice President