Professor Pictet on the Succession of Animals. 277 



closely allied, they cannot breed with each other, and that 

 if they are nearly allied, they give birth to mules, which 

 are steril, and incapable of becoming the progenitors of new 

 species ; every aberration from a type, by way of increase, is 

 thus immediately arrested. 



It is true, that naturalists have argued against these con- 

 clusions, from what takes place in domestic species, which 

 undergo considerable variations. Thus, oxen, horses, sheep, 

 pigs, and goats, form distinct races, and differ in one country 

 from another in colour, size, strength of bone, fatness, nature 

 of the covering, &c. Dogs present us with a still more re- 

 markable example ; their colour and size range within still 

 wider limits ; the form of the bones of the cranium undergoes 

 very considerable alterations ; and instinct itself varies with 

 these changes of form. These facts are true, but they seem 

 to me to furnish a conclusion exactly the reverse of that 

 drawn from them. Individuals most remote from the primi- 

 tive type never exhibit any real difference of form in the 

 essential organs ; the skeleton has always invariable charac- 

 ters, whether we regard the number of the bones, their 

 apophyses, or their relations ; the organs of nutrition, the 

 nervous system, everything, in a word, is subject to the same 

 rule. There is no marked difference except in the absolute 

 dimensions, which are well known to be so variable, and in 

 exterior circumstances still more evanescent ; and, with the 

 exception of these differences in the form of the cranium, 

 which are understood to be connected with differences of in- 

 stinct, and the direct result of education, it may be affirmed, 

 that none of the domestic animals, even in the most marked 

 varieties, ever lose the characters of the species. If we per- 

 ceive, then, that all the most energetic agents, change of 

 climate, habits, instinct, nourishment, have only produced, 

 though their action has lasted for ages, insignificant changes 

 which have been unable to alter the type of the species, are 

 we not authorised to infer, from this study of domestic ani- 

 mals, the permanence of species, rather than their transition 

 from one to another \ 



This is so much the more true, because the differences of 

 one fauna from another are very great ; and the object is not 



