24 INTRODUCTION. 



on the first chase knew how to attack the peccary, while an ordinary 

 dog is instantly killed by them. The barking of dogt is an acquired 

 hereditary instinct, supposed to have originated in an attempt to mu- 

 tate the human voice ; wild dogs, and domestic breeds become wild, 

 never bark, but howl. Cats, which so disturb civilised commui 

 by their midnight "caterwaul," in the wild state in Smith Am 

 are quite silent. 



These well-authenticated facts show to what extent a change of 

 external conditions may modify races of animals. Similar change* 

 may be found among our domesticated breeds. For instance the 

 breeds of sheep differ greatly in different countries ; but it is main- 

 tained that they all are varieties of one species. New breeds of 

 sheep are frequently formed, (and very much as the breeder wis 

 by crossing well-known races, or individuals having the peculiarities 

 which it is desired should be transmitted to the new breed. In the 

 same manner, he says, the numerous varieties of horses are without 

 doubt members of but one species; Blumenbach has remarked that 

 there is more difference between the skulls of the Neapolitan and 

 Hungarian breeds of horses, than between the skulls of the most 

 dissimilar forms of mankind. Some naturalists suppose the dog to 

 belong to the same species as the wolf; others derive him from the 

 jackal. With all their varieties, Frederic Cuvier believes the dogs 

 to embrace but one species ; he observes that if we make more than 

 one species w-e must make at least fifty, all distinguished by perma- 

 nent characters. Restored to the wild state, all these varieties 

 approximate to the type which may be supposed to have belong >< I to 

 the original species. Dogs differ in stature, in the shape of their 

 ears and tails, in the number of caudal vertebrae ; some have an 

 additional claw on the hind foot, and an additional false molar tooth 

 on one side ; the hair differs in color, texture and length, according 

 to the climate in the first instance ; but these differences become per- 

 manent like the corresponding peculiarities of the human races ; the 

 varieties of the dog tribe have become 'permanent varieties. 



This tendency to variation he ascribes not to accident, but a 

 " nisus formativus," a vital power " in virtue of which organiza- 

 tion receives a peculiar direction from external circumstances."' 

 Varieties in form and structure are found in the offspring of the 

 same parents which are transmissible, and thus lay the foundation 

 for different breeds ; but these variations are within certain limits, 

 and leave unaltered the specific character. It is not always easy to 

 decide what the specific characters are, and what qualities are vari- 

 able. The shape of the head furnishes the most remarkable in- 

 stances of variety and of characters distinguishing races ; the length 



