THE AMERICAN SPECIES. 



171 



latter at first consists of very deep cells which, however, under the 

 influence of the growing embryo, seem to flatten. The embryo then, 

 according to v. Kennel, enters into direct connection with this 

 epithelium, this change being accompanied by a peculiar alteration 

 in the shape of the former. The embryo, which is said to give off 

 fluid and to decrease in size, becomes applied to the epithelium as 

 a lenticular cell-mass (Fig. 79 A). The figures show the close nature 

 of the connection between the embryo and the epithelium, the latter 

 may, indeed, occasionally become detached from the Avail of the 

 uterus, and may surround the embryo as a special layer (Fig. 79 

 B, Ue). The central part of the embryo now rises from the surface 

 of the uterus, while the edges, which still remain in contact with the 

 latter, become somewhat approximated through these changes; the em- 

 bryo thus assumes 

 the form of a cap 

 open towards the 

 surface of the 

 uterus (Fig. 79 B). 

 From the surface 

 of the embryo a 

 few amoeboid cells 

 become detached ; 

 some of these be- 

 come applied to the 

 uterine epithelium 

 and, finally, these 

 amoeboid cells unite 

 and give rise to an 

 envelope which sur- 

 rounds the whole 

 embryo, and which 

 has been termed the 

 amnion or serosa 

 (v. Kennel, Fig. 



80, am). The margins of the cap-shaped embryo now become 

 approximated and fuse together, so that the embryo becomes a 

 closed vesicle. The embryo then grows out from the wall into 

 the cavity of the uterus ; its point of attachment narrows and 

 thus forms a stalk (Fig. 80, n). A proliferation of cells then 

 takes place at the base of the stalk, this growth being called by 

 v. Kennel the "embryonic placenta," Corresponding to this is a 



am 



Fig. 80.— Median section of a pear-shaped embryo of P. Ed- 

 wa ■ i. with amnion and uterine wall (after J. v. Kennel). 

 am, amnion; n, umbilical cord ; p.e, embryonic, p.u, uterine 

 placenta; Ue, uterine epithelium; Uw, wall of the uterus; 

 w, point of ingrowth. 



