138 Heredity. 



The body of a hybrid is in itself a new thing, and there- 

 fore in a certain sense unnatural, and a male hybrid is, 

 accordingly, more fitted for the production of gemmules 

 than a male of a pure or unmixed race. 



When a male hybrid is crossed with the female of 

 either pure species or with a third species, the children 

 are much more variable than those born from a hybrid 

 mother by a male of a pure species. \It would be diffi- 

 cult to devise an experiment better fitted than this to 

 show that variation is caused by the influence of the 

 male, and that the action of unnatural or changed con- 

 ditions upon the male parent results in the variability of 

 the child. 



The remarkable history of reciprocal hybrids is direct- 

 ly opposed to Darwin's view that the functions of the 

 two reproductive elements are essentially similar, for in 

 some cases it is impossible to breed from a female of one 

 species by the male of a second species, while the male 

 of the first species readily fertilizes the ovum of the 

 second and gives rise to fertile offspring. Even when 

 both crosses are fertile the one is often much more so 

 than the other. 



The hybrids of one cross often differ remarkably from 

 those of the other cross in general structure, and in 

 many cases they show, in addition to the common char- 

 acteristics of both parents, a tendency, more or less per- 

 fectly pronounced, to develop the recently acquired 

 characteristics of that species which is used as the fa- 

 ther. 



This law is often obscured by the appearance of rever- 

 sions, which are peculiarly apt to occur in hybrids, and 

 by the presence, in certain cases, of a tendency for each 

 parent to transmit its peculiarities to the hybrid, without 

 fusion with those of the other parent. But when we 



