What Jolly called vacuolization of epithelial masses is clear and resembles cell cords in rupturing oral membrane and septum transversum. Positive apoptosis markers in several closing plates of 2 embryos suggest that apoptosis has at least a limited role in removing some cells of ruptured pharyngeal membrane shreds. Further investigation of more frequent time stages might reveal transient apoptosis missed by our surveys. Apoptosis is often contemporary with cell division in a healthy embryo. It can remove cells that are no longer necessary, and it can help to limit hyperplasia.
Further study is necessary to clarify details of chick hindgut morphogenesis.
Conclusions Apoptosis has a role in formation of cell cords and cavitations in chick embryo hindgut and cloaca, and limited apoptosis may remove some cells of pharyngeal closing plate stubs. We are grateful for financial assistance from Sigma Xi, the Howard Hughes Foundation, the Casstevens Family Fund and the Hamilton College Academic Fund for Seniors. Data reported here come from the Senior Theses of Clark, Cooney, Crary, and Payzant and summer research of Briglin. Tables Literature Cited Boyden, E.A 1922. The development of the cloaca in birds, with special reference to the origin of the bursa of fabricius, the formation of a urodaeal sinus, and the regular occurrence of a cloacal fenestra.