VIIL] 



HOMOLOGIES. 



177 



logy," and especially of seiial, bilateral, and vertical 

 homology. 



The word "homology" indicates such a relation between 

 two parts that they may be said in some sense to be " the 

 same," or at least "of similar nature." This similarity, 

 however, does not relate to the use to Avhich parts are put, 

 but only to their relative position with regard to other 

 parts, or to their mode of origin. There are many kinds 

 of homology/ but it is only necessary to consider the 

 three kinds above enumerated. 



WING-BONES OF PTERODACTYLE, BAT, AND BIRD. 



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 man, the foreleg of the horse, the paddle of the 

 whale, and the wing of the bat and of the bird, are all 



1 For an enumeration of the more obvious liomological relationships see 

 Ann. and Mag. of Is at. Hist, for August IS 70, p. 118. 



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