?o THE POPULAR SCIENCE MONTHLY. 



i 



different species or to two different races. Well, the results of these 

 marriages obey the following laws, which are : 



When this union takes place between two animals belonging to 

 different species that is, when we attempt hybridization in the im- 

 mense majority of cases the marriage is sterile. Thus, for example, it 

 has been tried thousands of times and in all the world, to unite rabbits 

 and hares. It is said that they have succeeded twice. But these two 

 quoted facts are much more doubtful than the results of experiments 

 recently made by a man of true talent, skilled in the art of experi- 

 menting, and who believes in the possibility of these unions, who has 

 completely failed. Although he furnished the best conditions for suc- 

 cess, he was not more fortunate in his results than Buffon, and the two 

 Geoffroy Saint-Hilaires before him. 



So the rabbit and the hare are of such a nature that, although pre- 

 senting in appearance a great conformity, they cannot reproduce to- 

 gether. 



Such is the general result of crossing two different species. 



In many cases, the union of two individuals of different species is 

 fertile, but the offspring cannot reproduce. For example, I refer you 

 to the union of the ass and horse. This union produces the mule. All 

 the mules in the world are offspring of the jackass and the mare. 

 Now, these animals are numerous, for in Spain and in tropical America 

 they are much preferred for work to horses, because of their resistance 

 to fatigue. The hinny, less in demand, because less robust than the 

 mule, is the result of an inverse cross ; it is the offspring of the horse 

 and the ass. The hinny, like the mule, cannot reproduce its kind. 

 When we wish for either, we must have recourse to the two species. 



Finally, in extremely rare exceptions, the fertility persists in the 

 offspring, but it is much diminished. It diminishes still more in the 

 grandchildren, and it is extinguished in the third or fourth generation 

 at the most. This is the case when we unite the canary-bird with the 

 goldfinch. 



I might here accumulate a mass of analogous facts and details. 

 But over them all would appear a great general fact including them, 

 which is the expression of a law ; and here is this fact : notwithstanding 

 observations reaching back for thousands of years, and made on hun- 

 dreds of species, we do not yet know a single example of intermediate 

 species obtained by the crossing of animals belonging to different 

 species. 



This general fact explains how order is maintained in the present 

 living creation. If it had been otherwise, the animal world and the 

 vegetable world would be filled with intermediate groups, passing into 

 each other by insensible shades, and, in the midst of this confusion, it 

 would be impossible for even naturalists to discriminate. 



The general conclusion from all this is, that infertility is the lart 

 when animals of different species unite (Hybridization). 



