432 DEVELOPMENT OF FROG AND OTHER VERTEBRATA 



^ e.s. 



emb 



en-8p 



Fig. 227. — Development of the chick, as seen in median sections, showing 

 relation of embryo to shell, yolk, and embryonic membranes (cf. Figs. 224 



and 225). 



A, 2 days' incubation. B, 3 days. C, 10-14 days, al, allantois; al.c, allantoic cavity; 

 al.st., allantoic stalk; am, amnion; am.}., head and tail folds of amnion; ec-so., ectoderm 

 and somatic mesoderm; e.m., egg membrane; emb, embryo; en-sp, endoderm and splanch- 

 nic mesoderm; e.s., egg-shell; se, serosa or chorion; y, yolk. (Redrawn with modifica- 

 tions from Parker and Haswell, "Textbook of Zoology," copyright, 1921, by Macmillan and 

 Co., Ltd., reprinted by permission.) 



