526 THE POPULAR SCIENCE MONTHLY. 



Most nocturnal beasts have large eyes, but most bats have very- 

 small ones. 



This is perhaps due to the fact that bats in their flight are guided 

 by an extraordinarily delicate sense of touch so delicate as to seem 

 almost like a sixth sense. 



The external ear of most bats appears at first to be double a very 

 small one seeming to stand up inside the larger one. This appear- 



Fig. 1. Head of Laege-eaked Bat. t, Tragus. 



ance, however, is due merely to the very large development of a little 

 piece which in ourselves projects backward as a small rounded process 

 guarding externally the opening of our ear, and called the tragus. 



The food of our English bats consists of insects, and their teeth 

 bristle with sharp points, well suited to pierce the chitinous cases by 

 which the bodies of insects are protected. 



The stomach (like that of most beasts which live upon a purely 

 animal diet) is a simple, short, and rounded bag. 



The female is provided with a pair of milk-glands, situated on the 

 breast as in the apes and in man. 



The skeleton of the bat, when compared with those of some other 

 animals, affords an excellent example of how fundamental uniformity 

 of structure may underlie forms which are strikingly different in ac- 

 cordance with diverging habits of life. 



I have already called attention to the divergent aspects of the 

 aerial bat and the subterranean mole. Yet the bones of the flying- 

 organ of the bat closely resemble those of the burrowing organ of the 

 mole, save as regards the relative shapes and dimensions of the com- 

 ponent bones. But, while in the bat these bones are drawn out into 

 excessive length and tenuity, in the mole they exhibit the maximum 

 of concentration and robustness. Now, both these conditions are but 

 diverging manifestations of the human structure, and the same indeed 

 may be said of such extreme modifications as the fore-leg of the horse 

 or the paddle of the whale. 



But the bat and the mole present us with a special point of simi- 

 larity in their skeleton not found in the other animals named, including 

 ourselves. 



It is that the breastbone in both the bat and mole develops a me- 

 dian ridge or keel. This keel serves to afford additional surface for 

 the attachment of powerful muscles which pass thence to the arms, 



