“PLATE 4 
EXPLANATION OF FIGURES 
51 Median section of specimen No. 233. The ectodermal mass has become trans- 
formed into a vesicle, the lower wall of which has a small pore. X 167. 
52 This section lies ten sections to the right of the preceding. > 167. 
53 Section from blastocyst No. 329. This specimen was unfortunately 
crushed in transportation from the field to the laboratory, but the general rela- 
tions of the different parts can be made out. X 167. 
54 Section from specimen No. 289. The relation of the different parts is par- 
ticularly clear in this section. Note that the large extraembryonic cavity, which 
lies between the ectodermal vesicle and the mucosa, is entirely free from cells. 
x 85. 
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