448 THE PHYSIOLOGY OF REPRODUCTION 



first most marked in the lips and sides of the groove, and small 

 superficial haemorrhages occur, which detach the epithehum at 

 places. The tissue fluids also exude, and, along with the blood 

 and desquamated epithehum, form a coagulum around the' 

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

 uterine cavity. 



The epithehum of the crypt, after a preUminary prohfera- 

 tion such as Robinson describes in the mouse and rat, degenerates 



Sp. 



M.Som. 



Fig. 111. — The allantoidean diplo-trophoblast of Erinaceus. (From 

 Hubreoht's "The Placentation of Erinaceus europceus," Quar. Jour. 

 Micr. Scl, vol. xxx., 1889.) 



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

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



Tr.S. 



F.L. 



entirely, part being stripped off by extravasated blood and 

 part yielding to the infl.uence of the foetal ectoderm. Its 

 remnants and the other constituents of the coagulum probably 

 furnish pabulum for the ovum. The development of the de- 

 cidua proceeds rapidly, and the swollen hps 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 



