SENSORY ADAPTATIONS OF BATS. I 89 



the animal. It is necessary that a bat "remember" the points at 

 which it has been or a sense of direction would not help to orient 



it. 



The sense of direction in these bats may very probably be ac- 

 counted for, at least in part, by the high development of associa- 

 tive memory. A man can learn to go about a house and make 

 all the turns correctly through habit and with little or no depend- 

 ence on his senses. In his case it has probably required long 

 experience and many repetitions of the act. In the bats, an act 

 is learned very much more quickly and it is possible that one or 

 two repetitions may even be sufficient to render the performance 

 automatic. If this is true, the ability of the animals to find a 

 place at which they have once been, may be based neither on a 

 sixth sense, nor directly upon any of the five senses, but upon 

 associative memory and quickness in forming habit. 



The utility of a sense of direction to bats is so apparent as to 

 scarcely require discussion. It is impossible for sight to be of 

 any service in helping them to find their way in the caves. Out- 

 side noises do not go in far and (ew noises originate there, so that 

 hearing can be of little service in orienting them. 



It has been suggested (Blatchley, '96) that air currents may 

 guide them to the mouth of a cave, but this is to me inconceiv- 

 able. Not only does the direction of the current change in the 

 principal passages but there are always eddies in the chambers 

 and tortuous passages which would tend to confuse rather than 

 help them. The only odors are the constant ones characteristic 

 of a cave and since the bats pass through the air and not along 

 solid surfaces their own odor is not left with a sufficient degree 

 of permanence to be of service in guiding them. 



But if a bat have a sense of direction well enough developed 

 to guide it in retracing its way, it would have an immense advan- 

 tage over other animals of similar habits that lack such a sense. 

 Thus natural selection would foster and improve it. 



Conclusions. 

 Bats are separated from all other mammals by a number of 

 morphological peculiarities which are correlated with the adap- 

 tation for flight. 



