HYBRIDISATION. 89 



and of the Common Trout ; which could be done with greater 

 faciUty than the other, from the fact that the two species are 

 constantly found naturally co-existent in the same waters. 



Should any of these experiments result in the production of 

 hybrids, another interesting question would arise, as to whether 

 the males thus produced should be again capable of reproducing 

 their own species. Should this be the case, it would go very far 

 toward the breaking up the whole theory of distinct species of 

 this family, and proving thera to be merely accidental varieties, 

 casually produced at first, and having become, in process of 

 generations, capable of transmitting their own peculiar type to 

 their progeny — as is the case clearly with the various breeds of 

 dogs, horses, cattle, and other domestic animals, which, so long 

 as they are preserved unmixed, will produce like of like, but 

 which, if interbred with other close-kindred races, will produce 

 a mongrel, but not a hybrid — one, I mean, which is capable of 

 reproduction. 



Thus Shetland ponies breeding together will produce Shetland 

 ponies ; and blood-horses of the Arab stock, blood-horses. 



Intermix these, and you shall have a cross-bred offspring, 

 which is not, however, a hybrid, like the produce of a horse and 

 an ass ; for it is capable of breeding again, witli its own type, or 

 with either of the parent races, or with any other pure horse. 



And so of hounds, setters, greyhounds, and all the varieties 

 of domestic dogs, so long as they are interbred among them- 

 selves ; but the moment they are associated with the wolf, fox, 

 jackal, dingo, or any of the congenerous though distinct races, 

 they will breed with them, it is true, but the progeny will be 

 truly hybrid and barren. 



