FCETAL NUTRITION: THE PLACENTA 477 



ti'opholilast. The ca})illaries are distended and new vessels are 

 formed. This distension is at first most marked in the lips and sides 

 of the groove, and small superficial h;emorrhages occur, which detach 

 tlie epithelium at places. The tissue fluids also exude, and, along 

 with the blood and desquamated epithelium, form a coagulum around 

 the ovum. Part of it shuts off the entrance of the furrow from the 

 uteiine ca^^ty. 



The epithelium of the crj-pt, after a preliminary proliferation 

 such as Eoliinson describes in the mouse and I'at, degenerates 



'if'' -,'■>' 





S'p. JA/S'";/(. 



Fig. 138. — The allantoidean diplo-trophoblast of Eriaaceus. (From Hubrecht's 

 "The Placentation of Erinaceus eumpiens," (^n.ar. Juiir. J/ifi: Sciemv, 

 vol. XXX., 1889.) 



Tr.iS., Trophospoiigia ; Tr., trophoblast ; F.L., layer of fusiform cells ; 

 iSp., spaces in trophoblast ; 2[.Som., thin layer of somatic mesoblast. 



entirely, part l)eing stripped off by extravasated blood and part 

 yielding to the influence of the fcetal ectoderm. Its remnants and 

 the other c<jnstituents of the coagulum probaljly furnish palndum 

 for the ovum. The development of the decidua proceeds rapidly, 

 and the swollen lips of the groove fuse together to complete the 

 implantation cavity. The trophoblast is now in contact with 

 decidual tissue, of which the innermost zone consists of a stratified 

 layer of fusiform cells, best marked in the allantoic region (Fig. 138). 

 Whether they are maternal or fVctal in origin is not yet determined 

 They persist for a time, but disappear when the endothelial pro- 

 liferation occurs. Around the groove the tissue becomes looser by 

 an inciease in the size of the newly formed blood-spaces. The 



