422 THE CAUSES OF THE xi 



for the purposes of this argument if it were true 

 of only one of them, but there is, in fact, a great 

 number of such cases and that is, that, similar 

 as they may appear to be to mere races or breeds, 

 they present a marked peculiarity in the repro- 

 ductive process. If you breed from the male and 

 female of the same race, you of course have off- 

 spring of the like kind, and if you make the off- 

 spring breed together, you obtain the same result, 

 and if you breed from these again, you will still 

 have the same kind of offspring ; there is no 

 check. But if you take members of two distinct 

 species, however similar they may be to each other, 

 and make them breed together, you will find a 

 check, with some modifications and exceptions, 

 however, which I shall speak of presently. If 

 you cross two such species with each other, then 

 although you may get offspring in the case of 

 the first cross, yet, if you attempt to breed from 

 the products of that crossing, which are what are 

 called HYBRIDS that is, if you couple a male 

 and a female hybrid then the result is that in 

 ninety-nine cases out of a hundred you will 

 get no offspring at all ; there will be no result 

 whatsoever. 



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 



