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 tro'phospongia} interposed between the 

 blastocyst and the unaltered decidua. The trophoblast with its 

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

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



-Civ, . 









Tr> 



V If" 1 







Fig. 139. — Section inxitu of the ovum of Ertnarims (Hubrecht). 



Hy., Hypoblast ; Tr., trophoblast ; sp., spaces in the trophoblast, communi- 

 cating with the maternal blood-spaces {M.Hp.) ; /A, decidua ; TVs., 

 trophospongia. 



effective nutritional arrangement for the embryo before the vitelline 

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

 blood-spaces are ruptui'cd, and the blood pours out into the lacuna3 

 of the tropholilast, and circulates through them l>efore 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 dei'ived 



' "The trophospongia is a maternal cell-proliferation specially intended foi' 

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

 different genera " (Hubrecht). 



