48o THE PHYSIOLOGY OF REPRODUCTION 



proliferation of the trophoblast is confined to the allantoic region. 

 In the hedgehog the proliferation occnrs even in the oniphaloidean 

 region, which is vascularised liy the area vasculosa. Here the 

 vacuolated trophol.ilast is giai.lually inteiiocked with vascular 

 processes of the mesoblast, and yolk-villi, containing branches of the 

 vitelline vessels, are developed. The omplialoidean placenta thus 

 formed embraces about one-half of the cii'cumference of the 



B.y. 



B.V. 



Fig. 141. — Transverse section through the uterus of Horej- at a .stage when 

 the blastocysts are still in the oviducts. The coiled uterine glands {(-11.) 

 are massed together in the anti-niesometrial regions. The uterine lumen 

 ( U) is more or less _L-shaped. (From Hubrecht's " The Placentation of 

 the Shrew," Quar. Jnvr. J/icr. Science, vol. xxxv., 1894.) 



B. v., Blood-vessels ; e.m., circular muscle ; l./ii., longitudinal muscle. 



blastodeimic vesicle. With the union of the allantois and diplo- 

 tiophoblast, the circulation in the decidua reflexa deci'eases, and it 

 and the trophoblast in contact with it l)ecome membranaceou.s. 

 They project into the uterine cavity and oUiterate its lumen by 

 meeting, 1jut not fusing with, the mesometi'ial part of the uterine 

 mucosa. As in the Ijat, the circulation in tlie yolk-sac never ceases 

 entirely during pregnancy. 



The changes in the allantoidean trophoblast ai'e of the same kind, 

 but they occur later. It occupies a discoid area as in Rodents, l3ut 

 it is on the anti-mesometrial side, i.e. the primary deciilua reflexa is 



