654 



J. T. PATTERSON 



K- 



Tro 



17 



-Tro 



G C- 



Fig. 17 Median section of the ectodermal mass of specimen No. 332. This 

 specimen is just a little older than the preceding, and shows with great clearness 

 the manner in which the ectodermal mass is included within the entoderm. At 

 k is a knot-like growth from the trophoblast. Note that the ectodermal mass is 

 undergoing vacuolization to form a vesicle. X 245. 



Fig. 18 Median section of specimen No. 233. This shows the condition just at 

 the close of the formation of the ectodermal vesicle (see text for description). X 

 162. 



