DIVISIONS OF THE ANIMAL KINGDOM. lix 



te-rity. Some of the wild horsemen of the plains of South 

 America are, from infancy, continually on horseback, and 

 their limbs are observed to become slender and almost unfit 

 for walking, which characters reappear in the children of the 

 tribe. Amongst the causes, then, which tend to form va- 

 rieties, are to be numbered the habitudes of animals, whether 

 in the wild or domesticated state. 



Of the means by which the animal organism becomes 

 adapted to new relations we know nothing. We see that 

 within the limits of the specific form, animals become suited 

 to the nature and abundance of their aliment, to the condi- 

 tion of the external air with respect to temperature, humi- 

 dity, and density, and to the habits imposed upon them for 

 obtaining their vegetable food when they are herbivorous, or 

 capturing their prey when they feed on flesh ; but how or 

 why this is, we know no more than how or why animals as- 

 sume and preserve the form proper to their species. We 

 may well believe that species are called forth, and their 

 forms placed in the fitting relation with external nature, in 

 obedience to some grand system of Natural Laws, the results 

 of which we may hope in certain cases to trace, but of the 

 efficient cause of which we cannot hope to obtain a know- 

 ledge. But when we speak of causes in common language, 

 we do not, it is well known, refer to what metaphysicians 

 term efficient causes, but to the antecedents of those pheno- 

 mena which we term effects ; and it is in this sense that we 

 say that the causes of the varieties of animal species are 

 food, climate, habitudes, and the other agencies whose effects 

 we have the means of observing. 



But all the causes enumerated would not of themselves be 

 sufficient to form permanent varieties or breeds, were it not 

 for that other law of the animal economy by which animals 

 are enabled to communicate the characters acquired to their 

 progeny, and by which the latter are enabled to retain those 

 characters with more or less constancy. 



That animals which, from any cause, have acquired a pecu- 



