FCETAL NUTRITION: THE PLACENTA 



477 



trophoblast. The capillaries 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 haemorrhages occur, which detach 

 the 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 

 uterine cavity. 



The epithelium of the crypt, after a preliminary proliferation 

 such as Robinson describes in the mouse and rat, degenerates 



Tr.S. 



' - F.L. 



Sp. 



FIG. 138. The allantoidean diplo-trophoblast of Erinaceus. (From Hubrecht's 

 "The Placentation of /.'////</<<</$ europceus" Quar. /<//: .\ficr. Science, 

 vol. xxx., 1889.) 



Tr.S., Trophospongia ; TV., trophoblast ; F.L., layer of fusiform cells ; 

 Sp., spaces in trophoblast ; Jf.Som., thin layer of somatic mesoblast. 



entirely, part being stripped off by extravasated blood and part 

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

 the other constituents of the coagulum probably furnish pabulum 

 for the ovurn. 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 foetal 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 increase in the size of the newly formed blood-spaces. The 



