(3 INTIIODUCTOUY CHAPTER. 



differ from that of tlie dog in general, more than the different kinds 

 of dogs do from each other. The cranium is absolutely similar, and 

 so are all, or nearly all, the other essential parts ; and, to strengthen 

 still further the probability of their identity, the dog and wolf will 

 readily breed together, and their progeny is fertile. The obliquity of 

 the position of the eyes in the wolf is one of the characters in whicli 

 it differs from the dog ; and, although it is very desirable not to 

 rest too miu'h upon the effects of habit on structure, it is not 

 perhaps straining the point to attribute the forward direction of 

 the eyes in the dog to the constant habit, for many successive gener- 

 ations, of looking forward to his master, and obeying his voice." * 

 Such is the state of the argument in favour of the original 

 descent from the wolf, but, as far as it is founded upon the breed- 

 ing together of the wolf and dog, it applies also to the fox, which 

 is now ascertained occasionally to be impregnated by the dog ; but 

 in neither case we believe does the progeny continue to be fertile 

 if put to one of the same cross, and as this is now ascertained 

 to be the only reliable test, the existence of the first cross stands 

 for nothing. Indeed, experience shows us more and more clearly 

 every year, that no reliance can be placed upon the test depending 

 upon fertile intercommunion, which, especially in birds, is shown 

 to be liable to various excej^tions. Still it has been supported by 

 respectable authorities, and for this reason we have given inser- 

 tion to the above extract. 



* Bell's British Quadrupeds, pp. 19G-7. 



