624 



BIRDS. 



1-c s.g.c Ep 



Fig. 275. — Stages in development of chick. — After Marshall. 



1. Segmentation, superficial view of blastoderm. 



2. Vertical section of blastoderm. -£/5., Epiblast ; i.e. lower layer of 



cells ; s.g.c. , sub-germinal cavity ; y., yolk. 



