ACKNOWLEDGMENTS
I thank the organizers of the Symposium on Comparative
Gestation and Placentation in Vertebrates,
July 1-6,1991, for inviting me to participate. I appreciate
the stimulation that my graduate students
who have worked on the evolution of viviparity
(Lorrie Klosterman and Wendy Marlor) have given
me. I wish to acknowledge the support of the National
Science Foundation for my research on the
evolutionary biology of amphibians.