PERPETUATION OF LIVING BEINGS. Ill 



The reason of this is quite obvious in some cases ; 

 the male hybrids, although possessing all the external 

 appearances and characteristics of perfect animals, are 

 physiologically imperfect and deficient in the structural 

 parts of the reproductive elements necessary to genera- 

 tion. It is said to be invariably the case with the male 

 mule, the cross between the Ass and the Mare ; and 

 hence it is, that, although crossing the Horse with the 

 Ass is easy enough, and is constantly done, as far as I 

 am aware, if you take two mules, a male and a female, 

 and endeavour to breed from them, you get no offspring 

 whatever; no generation will take place. This is what 

 is called the sterility of the hybrids between two dis- 

 tinct species. 



You see that this is a very extraordinary circum- 

 stance; one does not see why it should be. The 

 common teleological explanation is, that it is to prevent 

 the impurity of the blood resulting from the crossing 

 of one species with another, but you see it does not in 

 reality do anything of the kind. There is nothing in 

 this fact that hybrids cannot breed with each other, to 

 establish such a theory ; there is nothing to prevent 

 the Horse breeding with the Ass, or the Ass with the 

 Horse. So that this explanation breaks down, as a 

 great many explanations of this kind do, that are only 

 founded on mere assumptions. 



Thus you see that there is a great difference between 

 " mongrels/' which are crosses between distinct races, 

 and " hybrids/' which are crosses between distinct 

 species. The mongrels are, so far as we know, fertile 

 with one another. But between species, in many cases, 

 you cannot succeed in obtaining even the first cross : 



