Till.] 



HOMOLOGIES. 



171 



ogy, 1 but it is only necessary to consider the three kinds 

 above enumerated. 



The term " homologous " may be applied to parts in two 

 individual animals of different kinds, or to different parts of 

 the same individual. Thus " the right and left hands," or 

 " joints of the backbone," or " the teeth of the two jaws," 

 are homologous parts of the same individual. But the arm 

 of a man, the fore-leg of the horse, the paddle of the whale, 

 and the wing of the bat and the bird are all also homologous 



WING-BOXES OF PTERODACTYL, BAT, AND BIRD. 



parts, yet of another kind, i. e., they are the same parts 

 existing in animals of different species. 



On the other hand, the wing of the humming-bird and 

 the wing of the humming-bird moth are not homologous at 

 all, or in any sense ; for the resemblance between them 

 consists solely in the use to which they are put, and is 

 therefore only a relation of analogy. There is no relation 

 of homology between them, because they have no common 

 resemblance as to their relations to surrounding parts, or 

 as to their mode of origin. Similarly, there is no homology 



1 For an enumeration of the more obvious homological relationships 

 see Ann. and Mag. of Nat. Hist, for August, 1870, p. 118. 



