HO CONDITIONS AFFECTING THE 



liarities, which have been developed from a common 

 stock, at least there is every reason to believe so. But it 

 is a most singular circumstance, that while you may run 

 through almost the whole series of physiological pro- 

 cesses, without finding a check to your argument, you 

 come at last to a point where you do find a check, and 

 ' that is in the reproductive processes. For there is a most 

 singular circumstance in respect to natural species — at 

 least about some of them — and it would be sufficient 

 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 reproductive process. If you breed 

 from the male and female of the same race, you of 

 course have offspring of the like kind, and if you 

 make the offspring 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 vou 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 what- 

 soever. 



