456 THE CAUSES OF THE 



XI 



as the members of any great natural group have 

 with a real or imaginary typical form. Now, we 

 know that all varieties of pigeons of every kind 

 have arisen by a process of selective breeding from 

 a common stock, the rock-pigeon ; hence, you see, 

 that if all species of animals have proceeded from 

 some common stock, the general character of their 

 structural relations, and of our systems of classifi- 

 cation, which express those relations, would be just 

 what we find them to be. In other words, the 

 hypothetical cause is, so far, competent to produce 

 effects similar to those of the real cause. 



Take, again, another set of very remarkable 

 facts, the existence of what are called rudi- 

 mentary organs, organs for which we can find 

 no obvious use, in the particular animal econ- 

 omy in which they are found, and yet which are 

 there. 



Such are the splint-like bones in the leg of the 

 horse, which I here show you, and which corre- 

 spond with bones which belong to certain toes and 

 fingers in the human hand and foot. In the horse 

 you see they are quite rudimentary, and bear 

 neither toes nor fingers ; so that the horse has 

 only one " finger " in his fore-foot and one " toe " 

 in his hind-foot. But it is a very curious thing 

 that the animals closely allied to the horse show 

 more toes than he ; as the rhinoceros, for instance : 

 he has these extra toes well formed, and anatomi- 

 cal facts show very clearly that he is very closely 



