THE CATEGORIES OF ANALOGY. 275 



the plan of structure of the Articulates ; so much so that 

 Oken does not hesitate to refer the Echinoderms to the 

 type of Articulates, mistaking their analogy for true homo- 

 logy. 



Class analogies. The ways in which, and the means 

 by which, the plan of structure of one class is carried 

 out, as compared with another class, frequently produce 

 striking analogies. For instance, among Vertebrates the 

 whole class of birds is winged; and wings constructed 

 like the wing of birds exists in no other class. Yet the 

 bats are also winged; and many fishes which are capable 

 of rising above the water are also described as winged. 

 But the wing of a bat is homologous to the foreleg of the 

 other mammalia, and only analogous to that of birds ; for 

 it exhibits the special homologies of the class of mam- 

 malia, and not those of the class of birds. 1 The same is 

 true of the so-called wings of the flying fishes, in which 

 the wing is a fin, homologous to the pectoral fin of other 

 bony fishes, and not constructed in the same way as the 

 wing of the bat or that of the bird. The wing of insects 

 is entirely different, and its analogy with the wing of 

 birds more remote, than that of the bat and of the flying 

 fish, inasmuch as it is not an analogy between members 

 of different classes of the same branch, but between two 

 classes of different branches, differing therefrom in the 

 plan of structure, and not only in the mode of execution 

 of one and the same plan. 



Ordinal analogies. As orders are founded upon the 

 complications of the structure which characterizes the 

 different classes, it is not likely that ordinal analogies will 

 occur between the different orders of one and the same 



1 As limbs of Vertebrates these homologous ; but as wings they are 

 two kinds of wings are, nevertheless, only analogous. 



