ALIMENTARY SYSTEM. 



501 



From the hindmost region of the gut, the allantois 

 grows out in all animals from Amphibians onwards. In 

 Amphibians it is represented by a cloacal bladder ; in the 

 higher Vertebrates it is a vascular foetal membrane con- 

 cerned with the respiration or nutrition of the embryo, or 

 both. 



S.c 



FlG. 267. Section through a young newt. 



c.t., Connective tissue; J5., epidermis; Z?., dermis ; S.C. spinal cord J M. t 

 muscle; TV., notochord ; S&., mesodermic sheath of notochord ; K. t 

 kidney; /., lung; S. t spleen; ST., stomach; Pe. t peritoneum; L. t 

 liver; d., duct of the pancre?* (/>); G.B., gall-bladder; V., dorsal 

 aorta. 



Cilia are very common on the lining of the intestine in 

 Invertebrates, but they are much rarer in Vertebrates. Yet 

 as they occur in Amphioxus^ lampreys, many fishes, Proto- 

 pterus, some Amphibians, and in embryonic Mammals, it 



