24 PHYSICAL INVESTIGATION. 



siders that the hybrids form a new permanent species. 1 This 

 is said also to apply to the domestic dog in relation to the wolf, 

 fox, jackal ; and also to the mulattoes, who always preserve the 

 same type, and should therefore be considered as a new spe- 

 cies ; whilst mongrels of tribes of the same stock (for instance, 

 of different Indo-Germanic peoples), preserve no fixed type, 

 but exhibit variable forms. In opposition to this, it is neces- 

 sary to state, that no reliable instance can be adduced of the 

 permanency of a hybrid race by in-breeding, least of all in 

 mammals; that the production of new independent types in 

 this manner is as yet extremely doubtful ; and that the adduced 

 examples, so far as they have been confirmed, can only be con- 

 sidered as individually extraordinary facts, which have but 

 little value in the attempt to lay the foundation of a new theory 

 of the laws of nature in the preservation of types, and so to 

 place the conception of species upon a different basis. 



All the examples which are usually adduced to prove un- 

 limited fecundity of hybrids, admit of a twofold interpretation. 

 If (according to Vogt) wolf, dog, and fox are prolific among 

 themselves, and if propagation is so much easier the nearer 

 we approach the highest animals, it may apart from the pro- 

 blematical second part of this proposition and of the doubtful 

 cases of dog and fox, the successful pairing of wolf and dog, 

 the hybrids of which propagated, in one instance, during four 

 generations (A. Wagner) be maintained that dog and wolf 

 do not belong to different, but to the same species. R. 

 Wagner accordingly lays down the proposition, 2 "that where 

 an intermixture of hybrids is observed (which can only with 

 certainty be asserted of wolf and dog, camels, goat, and sheep,) 

 the specific differences of the parent animals is, at least with 

 regard to mammals, doubtful." From his collection of hybrid 

 cases in the animal kingdom, it appears that in point of fact 

 there is no certain example of fecundity (not to speak of un- 

 limited fecundity) of hybrids between themselves, and only 

 individual instances of prolific intermixture with one of the 



1 Morton (" Hybridity in Animals and Plants/' p. 6, New Haven, 1847) con- 

 siders this as doubtful. 

 Prichard, Uebers, i, 449. 



