446 THE PHYSIOLOGY OF REPRODUCTION 



allantois consists of a tubular passage in the body wall and a 

 solid extra-embryonic stalk of mesoderm. It projects into the 

 ccelom and gradually extends, and becomes applied to the 

 mesoblast underlying the thickened part of the trophoblast, in 

 the spaces of which a circulation of maternal blood is established. 

 The trophoblast continues to attack and absorb maternal tissue 

 and blood, and to advance more deeply into the decidua, while 

 at the same time it is penetrated on the embryonic side by out- 



mes 



FIG. 110. Implantation cavity of the guinea-pig. (Duval.) 



mes, mesometrial (placental) border ; I, lumen of uterus, re-established anti- 

 mesometrially ; d.r., decidua reflexa; all, allantois ; am, amnion. 



growths of mesoblast containing branches of the allantoic 

 vessels. The tissues intervening between the maternal and 

 foetal blood-streams are entirely foetal ; they gradually thin 

 with the progress of gestation and the continued branching of 

 the mesodermal villi. 



Glycogen is contained in the decidual cells, but its variations 

 have not yet been investigated. It is of interest historically 

 that oxyhsemoglobin was demonstrated first in the umbilical 

 vein of a foetal guinea-pig by Schmidt. 1 The amounts of oxygen 



1 Schmidt, " Sauerstoffhamoglobin in Fo'tusherzblut," Cent. f. d. med. 

 Wise., 1874, No. xlvi. 



