A one-day symposium will be held at the annual meeting of the American Society of Zoologist in San Antonio, Texas, in December 1990. Animals are either oviparous (egg-laying) or viviparous (live-bearing). Viviparity, often considered a characteristic of mammals, has evolved independently in four of the five classes of vertebrates, namely fishes, amphibian, reptiles, and mammals. Birds are the sole exception. Evolutionary modification of the embryonic developmental program an maternal reproductive physiology facilitated the transition from oviparity to viviparity and form the basis of the new maternal-embryonic relationships. As a group, vertebrates offer unique opportunities for comparative and evolutionary studies of viviparity will be taken. Interactions among a diverse group is anticipated. Proceedings of the symposium will be published to provide a widely available reference for assessing progress in this developing field.
