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. X 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. 



068 



