2 Evolution and Adaptation 



similar to, but of course much smaller than, that made by the 

 mole. In both of these cases the adaptation is the more 

 obvious, because, while the leg of the mole is formed on the 

 same general plan as that of other vertebrates, and the leg of 

 the mole-cricket has the same fundamental structure as that 

 of other insects, yet in both cases the details of structure and 

 the general proportions have been so altered, that the leg is 

 fitted for entirely different purposes from that to which the 

 legs of other vertebrates and of other insects are put. The 

 wing of the bat is another excellent case of a special adap- 

 tation. It is a modified fore-limb having a strong membrane 

 stretched between the fingers, which are greatly elongated. 

 Here we find a structure, which in other mammals is used 

 as an organ for supporting the body, and for progression on 

 the ground, changed into one for flying in the air. 



The tails of mammals show a number of different adapta- 

 tions. The tail is prehensile in some of the monkeys ; and not 

 only can the monkey direct its tail toward a branch in order to 

 grasp it, but the tail can be wrapped around the branch and 

 hold on so firmly that the monkey can swing freely, hang- 

 ing by its tail alone. The animal has thus a sort of fifth 

 hand, one as it were in the middle line of the body, which can 

 be used as a hold-fast, while the fingered hands are put to 

 other uses. In the squirrels the bushy tail serves as a pro- 

 tection during the winter for those parts of the body not so 

 thickly covered by hair. The tail of the horse is used to 

 brush away the flies that settle on the hind parts of the body. 

 In other mammals, the dog, the cat, and the rat, for example, 

 the tail is of less obvious use, although the suggestion has 

 been made that it may serve as a sort of rudder when the 

 animal is running rapidly. In several other cases, as in the 

 rabbit and in the higher apes, the tail is very short, and is of 

 no apparent use ; and in man it has completely disappeared. 



A peculiar case of adaptation is the so-called basket on the 

 third pair of legs of the worker honey-bee. A depression 



