DEVELOPMENT OF THE CHICK. 607 



less and effete organ, is left behind in the cavity of the abandoned 

 egg-shell. The allantois is, therefore, strictly speaking, a foetal 

 organ. Developed as an accessory structure from a portion of the 

 intestinal canal, it is exceedingly active and important during the 

 middle and latter periods of incubation; but when the chick is 

 completely formed, and has become capable of carrying on an in- 

 dependent existence, both the amnion and the allantois are detached 

 and thrown off as obsolete structures, their place being afterward 

 supplied by other Organs belonging to the adult condition. 



