34 DISTINCTION BETWEEN SPECIES AND VARIETIES. 



of adapting themselves to changes in the circumstances of their 

 residence, mode of life, &c., that their utility to Man arises. 

 There is none which shows this more strongly than the Dog, 

 which is the companion of Man in every part of the globe, and 

 which presents more striking varieties of form than any other 

 species. Not only do the different races of Dogs vary in the 

 colour and quantity of their hair, but also in the proportions of 

 the different parts of their body (which is shown as much in 

 their skeletons as in the living animals), and even in their instincts, 

 which in most animals are invariable. How different, for ex- 



FIG. 2. CUBAN MASTIFF. 



ample, are the Greyhound and the Mastiff, the Bloodhound and 

 the Spaniel ! We should scarcely imagine that any period of 

 time, or external influences, could ever convert one into the other. 

 Yet the Zoologist has no hesitation in affirming, that they had a 

 common origin ; since it is found that their distinct forms are 

 preserved, only so long as they are matched in breeding with 

 forms of the same kind. For if the different races of Dogs are 

 allowed to breed promiscuously together, and escape from the 

 influence of Man, returning to their original savage mode of life, 

 the varieties gradually disappear, and the races all blend toge- 

 ther, after a few generations, into one common type, which 



