766 



PHYLUM CHORDATA : CLASS AVES — BIRDS 



Tl.S — 



p.s- 



Fig. 458. — Stages in development of chick.- -After Marshall. 



1. Segmentation, superficial view of blastoderm. 



2. Vertical section of blastoderm. Ep., Ectoderm (or epiblast) ; 



I.e., lower layer of cells; s.g.c. sub-germinal cavity ; y., yolk. 



