682 



BIRDS. 



Al 



6 



FIG. 378. Stages in development of chick. After Marshall. 



1. Segmentation, superficial view of blastoderm. 



2. Vertical section of blastoderm. E#., Epiblast ; 



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



*., lower layer 



