652 



J. T. PATTERSON 



a b d e f g b i J k ' 1 



En 



11 



1 2 



Fig. 10 Median section of the inner cell-mass of blastocyst No. 296. This 

 specimen shows with special clearness the formation of the entoderm. X 728. 



Fig. 11 A section taken slightly to the side of the center of the inner cell-mass 

 of blastocyst no. 311. X 596. 



Fig. 12 Outline of the marginal entodermal cells from blastocyst No. 300. 



Fig. 13 Marginal entodermal cells from blastocyst No. 320 (see plate 1). 



Fig. 14 Median section of the inner cell-mass of blastocyst No. 249. X 1190. 



Fig. 15 Median section of the embryonic spot of blastocyst No. 340. X 1190. 



Fig. 16 A section passing through the center of the ectodermal mass of speci- 

 men No. 316. The sections are not quite perpendicular to the surface of the mu- 

 cosa, and consequently the point of attachment does not show in this section 

 (see plate 2). X 218. 



