246 ON THE ORIGIN OF SPECIES 



species, follows according to Gartner the same laws. 

 When two species are crossed, one has sometimes 

 a prepotent power of impressing its likeness on the 

 hybrid ; and so I believe it to be with varieties of 

 plants. With animals one variety certainly often has 

 this prepotent power over another variety. Hybrid 

 plants produced from a reciprocal cross, generally re- 

 semble each other closely ; and so it is with mongrels 

 from a reciprocal cross. Both hybrids and mongrels 

 can be reduced to either pure parent-form, by repeated 

 crosses in successive generations with either parent. 



These several remarks are apparently applicable to 

 animals ; but the subject is here excessively compli- 

 cated, partly owing to the existence of secondary sexual 

 characters ; but more especially owing to prepotency 

 in transmitting likeness running more strongly in one 

 sex than in the other, both when one species is crossed 

 with another, and when one variety is crossed with 

 another 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 more resemble the ass than the horse ; but that 

 the prepotency runs more strongly in the male-ass than 

 in the female, so that the mule, which is the offspring 

 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 mongrel animals alone are born 

 closely like one of their parents ; but it can be shown 

 that this does sometimes occur with hybrids ; yet I 

 grant much less frequently with hybrids 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 

 almost monstrous in their nature, and which have 

 suddenly appeared — such as albinism, melanism, de- 

 ficiency of tail or horns, or additional fingers and toes ; 

 and do not relate to characters which have been slowly 

 acquired by selection. Consequently, sudden reversions 



