HYBRIDITY. 23 



not, as frequently is the case with sheep and goats, the cross 

 breed is not permanent, like the original types. This equally 

 applies to plants, though in them the return to the original 

 type may only occur after a series of generations, namely by 

 intermixture of the hybrids with individuals of the original 

 type. Induced by these phenomena, Buff on 1 includes in the 

 same species, all individuals which in the free state produce 

 young possessing between themselves an unlimited prolificacy. 



This criterion of species, although approved of by F. Miiller 

 and others, has recently been much canvassed. It was already 

 contested by Rudolphi, 2 who asserted that not only were there 

 many hybrids produced in the natural state, but that prolifi- 

 cacy was the rule as regards the hybrids of mammals. Though 

 this assertion is manifestly far beyond the truth, still there 

 stands the remarkable fact that crossings between remote 

 species, and even between different genera, are frequently pro- 

 lific, (ass or horse with horned cattle, stag and cow, bear or 

 buck with a bitch, dog and cat, roe and sheep, swan and 

 goose), whilst the hybrids of more proximate species are not 

 so : jackal and dog, ox and buffalo, hare and rabbit, 3 (as asserted 

 by some), resist all attempts at crossing them. We are certainly 

 yet a long way off from concluding, from the above individual 

 phenomena, the unlimited prolificacy of cross-breeds; they 

 serve only to draw our attention to the fact that we are, as 

 yet, entirely ignorant of the law upon which the success or 

 failure of cross-breeding depends ; but this has not deterred 

 some writers from the attempt to clear this gap. Thus, Bory 

 assigns to the hybrids of the sheep and wild ass (onager), of 

 wolf and dog, siskin and linnet, unlimited prolificacy, though 

 he cannot assert the same as regards the mule. 



Desmoulins declares the herds of cattle of the United States, 

 beyond the Alleghanies, to be the progeny of the American 

 bison and European cattle, the former having a differently 

 formed skull and two ribs more than the latter ; and he con- 



1 (Euvres in 4to, iv, p. 386 : Succession const ante d'individus semblables et 

 qui se reproduisent. 



2 Beitrage zur Anthropol., 1812. 



3 The Leporine, a hybrid of hare and rabbit, may now be seen in the gar- 

 dens of the Zoological Society. ED. 



