ABORTED ORGANS. 8 1 



other cases, they have not totally disappeared, but 

 remain as rudiments. The splint bones of the 

 horse's foot, as abundantly proved by fossils, are 

 remnants of toes, formerly well developed and func- 

 tional in the horse family, but which have become 

 useless and consequently reduced. Of the five toe? 

 which were formerly present, two have completely 

 disappeared, two remain as rudimentary splint bones, 

 while the fifth is well developed and functional. 

 And similarly through the simple influence of dis- 

 use nearly all cases of atrophied organs are simply 

 and naturally accounted for. 



But this explanation, though unquestionably su- 

 perior to the other, is not yet quite satisfactory, and 

 meets difficulties in at least two points. First, it 

 will not explain all rudimentary organs. Each sex 

 possesses rudiments of organs found in the other. 

 The mammae on the breasts of the male mammal 

 are truly rudimentary organs, and their presence 

 can hardly be explained by inheritance. This dif- 

 ficulty is quite similar to the one considered above 

 in regard to serial homology. We can hardly sup- 

 pose that the male mammal ever possessed mammae, 

 which through disuse have become aborted, although 

 even this position is held by some naturalists, who 

 instance the fact that it is the male in many 

 species who cares for the young. But this hypoth- 

 esis will not be received as an answer by many ; and 

 we must admit that such rudimentary organs are 

 unexplained, unless we say that one sex has a tend- 

 ing to inherit the characteristics of the other sex. 

 A second difficulty, somewhat more serious, is to 



