44 



THE BOOK OF NATURE STUDY 



But there are yet other peculiarities about the bats. They 

 are, it will be remembered, creatures of the night, emerging from 

 their hiding-places only after the shades of evening have fallen. 

 Now animals which have adopted this habit do one of two things 

 they either develop enormously large eyes, or suppress them 

 altogether, developing a delicate sense of touch by way of com- 

 pensation. The eyes of the bat appear to be well on the way 

 towards suppression, for they have become reduced to mere pin- 

 points, which probably serve but for little else than to distinguish 



a 



FIG. ii. a, Fore-limb (wing) of a bird ; l>, fore-limb (wing) of a bat ; c, fore-limb 

 (arm) of a man. These three figures are contrasted to show the two widely 

 different ways in which an originally five-fingered fore-leg has been transformed 

 to fulfil the purposes of flight on the one hand, and of a grasping organ on the 

 other. I. ii. in. iv. v. = digits (fingers) 1-5. In the bird the thumb (digit I.) 

 and the third finger (digit III.) have been greatly reduced. 



light from darkness. Compensation for the loss of sight has 

 been found in an excessive sensitiveness of the wing-membranes 

 and the folds of skin which form the external ears. Some species 

 have developed additional skin-folds in the region of the nose, 

 which have very often a very complex character, as may be 

 seen, for example, in the horse-shoe bat. Bats which have 

 been deprived of sight have been known to make their way about 

 a darkened room in which had been placed a maze of entangle- 



