PLATE 2 
EXPLANATION OF FIGURES 
Photomicrographs of living eggs; in Ringer’s solution by reflected light; in 
the eight figures two litters are shown from each of four animals; all figures 
X 8, except fig. 8, which is X 2. 
1 Litter No. 293; 4-celled eggs. 
2 Litter No. 293’; interval 3} days; young bilaminar blastocysts. 
3 Litter No. 346; bilaminar blastocysts. 
4 Litter No. 346’; interval 93 hours; early primitive-streak stage. 
5 Litter No. 343; 1 mm., bilaminar blastocysts. 
6 Litter No. 343’; interval 7 hours and 20 minutes; bilaminar blastocysts 
just preceding first proliferation of mesoderm. 
7 Litter No. 298; unilaminar blastocysts of 60 to 120 cells with entoderm 
mother cells. 
8 Litter No. 298’; interval 34 days; vesicles in opened uterus; primitive 
streak and short medullary groove. X 2. 
100 
