1-c s.g.c. Ep 



Fig. 2i8. — Stages in development of Chick. (After Marshall.) 



1. Segmentation, superficial view of blastoderm. 



2. Vertical section of blastoderm ; Ep.-, epibla.st ; I.e., lower layer of cells ; s.g.c, seg- 

 mentation cavity ; y., yolk. 



3. Diagrammatic surface view; a.p., area pellucida; a.o., area opaca ; n.p., neural 

 groove ; p.s., primitive streak. 



4. Diagrammatic surface view at later stage; ap., area pellucida; a.o., area opaca; 

 m.s., mesoblast segments ; p.s., primitive streak. 



5. Cross section ; s.c, spinal cord ; s.g., rudiment of spinal ganglia ; ^V., notochord ; 

 vi.p., mesoblastic plates ; A.., aorta ; avi., amnion fold. 



6. Embryo ; C(^., cerebellum ; /^.,ear; //"., heart ;_/;/., fore limb ; h.l.,\\mAX\mh\ y.s., 

 stalk of cut-off yolk sac ; Al., allantois ; E., eye ; c, cerebrum. 



