478 THE PHYSIOLOGY OF REPRODUCTION 



endothelium lining them is swollen and deep, and the cells bulge into- 

 the lumen. Near the ovum the endothelium proliferates and forms 

 an enormous cell-mass, the trophospongia, 1 interposed between the 

 blastocyst and the unaltered decidua. The trophoblast with its 

 lacunse, and the trophospongia with large blood-sinuses together form 

 the trophospherc, which, along with the maternal blood, represents an 



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* tfrZfj ., ' 



M 

 ,,. *-X3gm 



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Mr 



/> 



>it*^ ' TVs. 

 to 



Trs. 



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FIG. 139. Section in situ of the ovum of Ennaccus (Hubrecht). 



Hi/., Hypoblast ; TV., trophoblast ; sp., spaces in the trophoblast, communi- 

 cating with the maternal blood-spaces (M.8p.) ; /)., decidua ; Trs. f 

 trophospongia. 



effective nutritional arrangement for the embryo before the vitelline 

 or allantoic circulation is established (Fig. 139). Many of the 

 blood-spaces are ruptured, and the -blood pours out into the lacunse 

 of the trophoblast, and circulates through them before returning into 

 the maternal veins. At this stage the trophospongia is separated 

 from the external decidua by rows of fusiform cells. 



As in the mouse, in which, however, the trophospongia is derived 



1 " The trophospongia is a maternal cell-proliferation specially intended for 

 the fixation of the blastocyst. It shows a different histological evolution in 

 different genera " (Hubrecht). 



