SENSORY ADAPTATIONS OF BATS. 173 



Hearing undoubtedly aids the bat to secure the flying insects 

 on which it feeds and thus has been developed to a high degree 

 by natural selection. The perception of a stationary object is 

 probably due to the condensation of the air between the flying 

 bat and the solid body that it is approaching. If hearing is rela- 

 tively as well developed in a bat as smell is in a dog it is not dif- 

 ficult to imagine that condensation of the air so slight as to be 

 imperceptible to the human ear will arouse sensations on the 

 auditory end organs of the bat. It is reasonably certain that the 

 highly modified external auditory apparatus of a bat has some 

 important function, the exact nature of which is unknown. 

 Flower and Lydekker ('91) state that the function of the tragus 

 is probably to " cause undulations in the waves of sound and so 

 intensify and prolong them." As far as I am aware, no attempt 

 has ever been made to more definitely define the function of that 

 organ. It seems to me highly probable that it also has a selec- 

 tive action, perhaps destroying waves of certain kinds and inten- 

 sifying others. 



It is necessary to bear in mind in discussing the senses of the 

 lower animals that it is impossible to form any adequate concep- 

 tion of the sensations and mental life of the lower animals on the 

 basis of our own. If a piano recital is incomprehensible to a 

 Hottentot, or a snake dance to a cultured Caucasian, how much 

 less can either hope to understand the perceptions aroused in the 

 brain of a hound that scents a fox, or the mental processes of a 

 bat as he circles among the tree tops in pursuit of insects ? 



The body of a bat is covered with fine hairs of a peculiar 

 structure. The membranes also support hairs, the number vary- 

 ing considerably in the different species. These hairs are sup- 

 posed to have a sensory function. No means was devised for 

 completely destroying the sense organs located in them without 

 seriously injuring the animals. But they were coated with thick 

 vaseline which pasted the hairs together and made them less sen- 

 sitive to slight stimulation. 



The experiments under these conditions yielded the following 

 results : Five examples of M. lucifugus with the hair so coated 

 struck 36.4 per cent, of chances. The same five normal struck 

 28.8 per cent. Five M. siibiilatJis struck 39.6 per cent, of trials 



