126 GOOD FEOII CROSSING. Chap. XYIL 



extent analogous with that of self-impotent plants which. 

 cannot be fertilised by their own pollen, but are perfectly 

 fertile with pollen of any other individual of the same species. 

 The fact of infertility of this peculiar nature being one of the 

 results of long-continued interbreeding, shows that inter- 

 breeding does not act merely by combining and augmenting 

 various morbid tendencies common to both parents ; for 

 animals with such tendencies, if not at the time actually ill, 

 can generally propagate their kind. Although offspring 

 descended from the nearest blood-relations are not necessarily 

 deteriorated in structure, yet some authors believe that they 

 are eminently liable to malformations ; and this is not im- 

 probable, as everything which lessens the vital powers acts 

 in this manner. Instances of this kind have been recorded 

 in the case of pigs, bloodhounds, and some other animals. 



Finally, when we consider the various facts now given 

 which plainly show that good follows from crossing, and less 

 plainly that evil follows from close interbreeding, and when 

 we bear in mind that with very many organisms elaborate 

 provisions have been made for the occasional union of distinct 

 individuals, the existence of a great law of nature is almost 

 proved ; namely, that the crossing of animals and plants 

 which are not closely related to each other is highly beneficial 

 or even necessary, and that interbreeding prolonged during 

 many generations is injurious. 



