654. J. T. PATTERSON 
ECS LAS Der 
ETA 
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. 
