294 



ANIMAL MOVEMENT 



a hint as to the way in which the flying-membranes of bats have 

 been evolved. For in this creature we find that though the 

 fingers are not elongated they are webbed, and the steering- 

 power which is undoubtedly possessed may be associated with 

 up-and-down movement of the arms. Here we probably have 

 the first beginnings of the power of flight, which essentially 

 depends upon movements of the kind. The webbed hands, 

 being the parts brought down upon the air with greatest vigour, 

 would have a very special value even at an early stage. Hence 



we are able to picture 

 /'^ --^^ /iS^*=^ a gradual elongation 



of digits, with corre- 

 sponding increase of 

 the webs between 

 them, the lateral para- 

 chuting membrane be- 

 ing at the same time 

 gradually merged in 



the 



en 



laro-j 



ng 



hand. 



Fig. 830— Skeleton of Bat. cl.. Collar-bone; 

 7- forearm; I-v, 



We may, in fact, re- 

 gard (see fig. 830) that 

 part of the Bat's wing 

 external to the little 

 finger ( V) as being the greatly-developed webbed 

 hand, while the part between this and the body 

 is the old lateral parachuting fold. 

 Considering the very considerable powers of flight which Bats 

 possess, it is not surprising to find that they have a very wide 

 geographical distribution. Speaking of the small forms which 

 make up the largest family ( Vespertilionidcs) of the order, Wallace 

 says (in The Geographical Distribution of Animals): — "They 

 range over almost the whole globe, being apparently only limited 

 by the necessity of procuring insect food. In America they are 

 found as far north as Hudson's Bay and the Columbia river; 

 and in Europe they approach, if they do not pass, the Arctic 

 circle. Such remote islands as the Azores, Bermudas, Fiji 

 Islands, Sandwich Islands, and New Zealand, all possess species 

 of this group of bats, some of which probably inhabit every 

 island in warm or temperate parts of the globe." As to powers 

 of flight, the same author remarks that Bats are capable of tra- 



