164 - Edwin G. Cotikliu. 



Right or Left Half Embryos; 64-CELLs to Gastrula. 



Figs. 25, 26. Fixed and stained half embryos; spurted in the 2-cell stage and fixed 2 hours later. 

 Fig. 25. Right half of 64-76-cell stage, dorsal view. The neural plate cells (A^.^, A^-^^ A*.'*, A*-'6) 

 have just divided, the chorda cells (A^-', A'.') are dividing. The position of the cells A^-', A'-^ is 

 slightly abnormal, {y. Fig. 6.) Fig. 26. Left half of 64-76-cell stage, ventral-posterior view. 



Figs. 27, 28. Right half of embryo in about i8o-ce]l stage; spurted in the 4-cell stage and fixed 

 2^ hours later. Fig. 27. Dorsal view; the large endoderm cells lie above the level of the other cells 

 and form an exogastrula; some of the yellow cells (stippled) still lie at the surface while others are 

 covered by endoderm cells. Fig. 28. Ventral view of similar embryo. 



Figs. 29, 30. Living right half embryos, dorsal view, showing the endoderm cells forming exogas- 

 trulae and the yellow crescent cells at the surface. 



