SENSORY ADAPTATIONS OF BATS. 157 



flew near enough to this to feel the splashing water and then 

 turned and flew repeatedly across the room, keeping near the 

 floor and frequently giving the floor an audible bump with its 

 opened lower jaw. The other time there was no running water 

 in the room which could have set off the impulse, but there was 

 standing water which it may or may not have approached. On 

 both occasions there was a good light, either artificial or daylight, 

 and the floor was of a dull, yellowish brown color which might 

 look to an animal flying -over it like water of a pond on a starlit 

 night. 



The evidence at hand is not sufficient to prove the point, but 

 it seems probable that sight may be the sense by which water is 

 usually distinguished, but that moisture-laden air, rising from a 

 body of water to a bat flying above it, also helps the animal to 

 locate water. 



I am unable to say whether bats ever drink in the caves. In 

 most places there is so much moisture that they probably do not 

 become thirsty. There is no evidence to show that they ever eat 

 in the caves. Some insects could be obtained there but the 

 quantity would be inconsequential as compared with the number 

 of bats to eat them. The lack of sufficient food is doubtless the 

 only reason that they have never become true cave dwellers. 



Locomotion. 

 Bats are more helpless on their feet than most birds. This is 

 in part due to the mechanical impediment of the flying membrane, 

 and in part to the skeletal modification outlined in the section on 

 morphological characters. As a result of these changes in form 

 the animals cannot support themselves on their hind limbs alone, 

 as do birds and man, nor can they rest upon the terminal part of 

 the fore limbs. When walking upon a horizontal surface a bat 

 rests upon the sole and claws of the hind foot and upon the car- 

 pus and thumb of the fore limb. The phalanges are usually 

 folded backward along the fore arm, as when at rest, though the 

 wing is sometimes slightly expanded. The tail and interfemoral 

 membrane are curved forward under the body and both the tail 

 and the wing may touch the floor at times. The body is elevated 

 so that it clears the floor. The limbs are moved as in other 



