PLATE 8 
EXPLANATION OF FIGURES 
Photomicrographs showing progress in entoderm formation and polar differ- 
entiation; figs. 1, 3, 5, and 6, photographed in the living state in Ringer’s solu- 
tion by transmitted light. 
1 An egg of litter No. 356, showing opaque embryonic area and thin tropho- 
blastic area. XX 82. 
2 Blastocyst No. 356 (7); 16th section (total 32); Flemming 54; X 200; com- 
pare with fig. 1. 
3 One of two identical eggs from litter No. 349; opaque embryonic area to 
the left; compare fig. 12, pl. 17. X 36. 
4 Egg No. 349 (5), the least developed egg from litter No. 349; polar differ- 
entiation is well under way; retarded in development as compared with fig. 3; 
14th section (total 25); Bouin, 54. X 200. 
5 Egg No. 344 (7), lateral aspect, as seen alive; the longitudinal section of 
this egg is shown in fig. 7. x 82. 
6 Egg No. 344 (8), as viewed with opaque embryonic area uppermost. X 82. 
7 Egg No. 344 (7), in section, seen alive in fig. 5; 10th section (total 23) ; 
Flemming; 5 pl. X 500. 
