490 BIOLOGY. 



result of the lungs being injected with venous blood, 

 and thus of necessity ensues. When, on the contrary, 

 cases arise causing pulmonary suffocation, the blood then 

 regurgitates to the umbilical vessels, in order to reach 

 the original branchia or placenta. 



3023. Another process of respiration is found to take 

 place in the vessels of the allantois. Its fluid becomes 

 oxydized and penetrates through the urinary bladder into 

 what have been called primordial kidneys. This kind of 

 respiration through the anus is persistent in many Worms 

 and larvae of Insects. 



3024. Finally, there is a respiratory process on the 

 body of the embryo itself through the branchial apertures 

 on its neck ; these in the Frogs and Salamanders still 

 continue visible after their exclusion from the egg. This 



I oxygen must be derived from the foetal water. 



3025. Without doubt also the vitelline vessels respire, 

 and thus each vegetative system has its own process of 

 respiration. The intestine respires through the vitelline 

 vessels, the vascular system through the vessels of the 

 chorion, the sexual system through those of the allantois, 

 the integument through the branchial apertures. The 

 lungs belong to, and perform respiration for the whole 

 body. 



Decay of the Developmental Organs. 



3026. When all the organs are developed, the intes- 

 tines are drawn together with the vitellus into the ab- 

 domen. The chick is still nourished several days after 

 exclusion from the egg by the vitelline mass, which 

 passes through the vitelline canal into the intestine. 

 The vitelline membrane subsequently becomes flaccid, 

 and finally disappears through maceration. In the Mam- 

 malia the umbilical vesicle separates at an earlier period 

 from the intestine, and continues to lie in the umbilical 

 cord. 



3027. The secernent point of the vitelline membrane 

 or of the umbilical vesicle is the coecum. 



3028. There are therefore two intestinal systems, 



