250 Elementary Biology. 



and especially the first appearance of that character in its 

 embryology. As we shall afterwards find, segmentation and 

 the formation of mesoblastic somites are features of the 

 highest importance in the morphology and development of 

 the higher types. Again, we may note the epiolastic origin 

 of the nervous system, also almost invariably the rule in the 

 animal kingdom. The origin of the coelom, the formation of 

 the enteron, and its differentiation into an alimentary canal 

 are also worthy of attention if any generalised view is to be 

 obtained of the mode of origin of the various morphological 

 types of animal organisation. 



