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 
