THE HISTORY OF ANATOMICAL SCIENCE 301 



with ordinary mammals. Therefore, zoologists 

 put the whale into the same class as the mam- 

 mals, not into that of the fishes. But this conclu- 

 sion implies the assumption that animals should 

 be arranged according to the totality of their 

 resemblances. It means that the likenesses in 

 structure of whales and mammals are greatly 

 more numerous and more close than the likenesses 

 between whales and fishes. The same argu- 

 mentation applies to the likeness between bats 

 and birds. These are few and superficial, while 

 the resemblances between bats and ordinary 

 mammals are innumerable and profound. There- 

 fore bats go into the class Mammalia, not into the 

 class Aves. In these cases, the estimation of the 

 relative value of resemblances is easy enough ; but, 

 in respect of the lesser groups, the problem offered 

 frequently greater difficulties. Even Cuvier, 

 misled by certain superficial resemblances, could 

 refer the acorn-shells and the barnacles to the 

 class of Mollusks. 



Thus, in course of time, there arose in the 

 minds of thoughtful systematists a distinction be- 

 tween ' analogies ' and ' affinities ; ' and, in those 

 of the philosophical anatomists, a corresponding 

 discrimination between 'analogous' and 'homo- 

 logous ' structures. Outward resemblances of the 

 character of those which obtain between a whale 

 and a fish, a bat and a bird, were said to be mere 

 analogies, and were properly regarded as of no 



