REPRODUCTION 



737 



Iditional material in the same way. The period during which it does so 

 , however, very limited. 



The Vitelline Circulation. The vitelline circulation, which in oviparous 



ttimals, e.g., the chick, is of primary importance because of the large 



mount of food stored in the vitellus or yolk, is in mammals of relatively 



ight importance because of the limited supply of food in the vitellus. It 



nevertheless present in early stages. 



The Allantoic Circulation which in oviparous animals is also of primary 

 nportance in the latter half of the incubation period both as an absorption 



eta 









. 



superi'or vencavx i Hepatic vein. ^.Venaporte. ,. #. Pulmonary vem. 

 ve j n< (From Kollmann.} 



and respiratory apparatus is also present in mammals to a slight extent, 

 but it is merely a transition stage in the development of placenta! circulation 

 The Placental Circulation.-The development of the fetal or placental 

 circulatory apparatus by which the fetus obtains its food supply and nece: 

 sar} oxygen and frees itself from carbon dioxid has been alluded to ma 

 foregoing paragraph relating to the formation of the placenta. After the 

 blood-vessels of the embryo, the umbilical arteries and vein have come into 

 and physiologic relations with the uterine blood-vessels, the 

 nSrials and the oxygen are derived entirely from the maternal 



47 



