34 THK MAMMALIA. 



1 with those of the present reptiles (<y/. the 



allantoi>i. The- earliest traces of mammals from 



>ic rocks lead us to suppose a long series 



of predecessors, and direct our thoughts to further 



nnfathomrd depths of the earth's development. 



It is a din". -rent matter as regards those charac- 



liicli the systematic zoologist makes use 



of. first of all in distinguishing the subdivisions of 



tin ijroup, the differences of the instruments of 



locomotion, more especially of the outer limbs, 



bands and feet, and also of the dentition. The 



function of propagation exercises universally a 



more subordinate influence upon the outward 



trance and the general habitus of the animal, 

 than docs nutrition. The manner in which its 

 food is acquired gives the organism its peculiar 

 .-lamp, apart from the outer covering that acts as 

 a protection against its enemies and climatic 

 changes, and varies accordingly; and this stamp 

 -ed chiefly in the formation of the limbs 

 and tin dt ntition of the mammal. Cuvier's words, 

 (iivc me a tooth, and from it I will build up the 

 whole animal,' are to be taken seriously ; thoy 

 may b- applied to almost every other individual 



>f tin- >k -It-ton, and above all to the extremi- 



t the limbs. The last portion of a finger will 



