266 THE ORIGIN OF SPECIES 



crossed with another and when one variety is crossed with an- 

 other variety. For instance, I think those authors are right who 

 maintain that the ass has a prepotent power over the horse, so 

 that both the mule and the hinny resemble more closely the ass 

 than the horse; but that the prepotency runs more strongly in 

 the male than in the female ass, so that the mule, which is an off- 

 spring of the male ass and mare, is more like an ass than is the 

 hinny, which is the offspring of the female ass and stallion. 



Much stress has been laid by some authors on the supposed 

 fact, that it is only with mongrels that the offspring are not in- 

 termediate in character, but closely resemble one of their parents: 

 but this does sometimes occur with hybrids, yet I grant much 

 less frequently than with mongrels. Looking to the cases which 

 I have collected of cross-bred animals closely resembling one 

 parent, the resemblances seem chiefly confined to characters al- 

 most monstrous in their nature, and which have suddenly ap- 

 peared — such as albinism, melanism, deficiency of tail or horns, 

 or additional fingers and toes; and do not relate to characters 

 which have been slowly acquired through selection. A tendency 

 to sudden reversions to the perfect character of either parent 

 would, also, be much more likely to occur with mongrels, which 

 are descended from varieties often suddenly produced and semi- 

 monstrous in character, than with hybrids, which are descended 

 from species slowly and naturally produced. On the whole, I 

 entirely agree with Dr. Prosper Lucas, who, after arranging an 

 enormous body of facts with respect to animals, comes to the 

 conclusion that the laws of resemblance of the child to its parents 

 are the same, whether the two parents differ little or much from 

 each other, namely, in the union of individuals of the same vari- 

 ety, or of different varieties, or of distinct species. 



Independently of the question of fertility and sterility, in all 

 other respects there seems to be a general and close similarity in 

 the offspring of crossed species, and of crossed varieties. If we 

 look at species as having been specially created, and at varieties 

 as having been produced by secondary laws, this similarity would 

 be an astonishing fact. But it harmonizes perfectly with the view 

 that there is no essential distinction between species and varieties. 



SUMMARY OF CHAPTER 



First crosses between forms, sufficiently distinct to be ranked 

 as species, and their hybrids, are very generally, but not univer- 

 sally, sterile. The sterility is of all degrees, and is often so sHght 

 that the most careful experimentaUsts have arrived at diamet- 



