Endpoints in the development of chick embryos

Although the use of mammalian embryos must remain the ideal for most teratological studies, non-mammalian embryos offer certain advantages. Their independence from the mother makes it possible to study the effects of reagents directly on the embryo without having to take possible placental effects into consideration, and it enables manipulations to be carried out more easily. In the early embryonic stages the cells of Xenopus and the chick are larger than those of the mouse, and these non-mammalian embryos tend to be bigger than those of the mouse at comparable stages of development. Attention is focused on the chick embryo as a useful experimental animal in the study of teratological effects. Consideration is given to some of the critical stages in embryogenesis as well as to the culture techniques available.