1/6 WALTER LOUIS HAHN. 



To determine whether there was any avoidance or whether the 

 animals hit or missed by accident, a ball of cotton with one diam- 

 eter equal to the expanse of the bat and the other slightly 

 smaller, to compensate for the upward stroke of the bat's wing- 

 when the distance from tip to tip is somewhat less, was thrown 

 at random at the tapes. The ball struck 82 per cent, of the 

 trials, or approximately the calculated number, as against the maxi- 

 mum of 60 per cent, for the bats. 



The difference is more apparent when we separate the " hits " 

 from the " touches." For the ball the " hits " were 48 per cent, 

 of the total chances and "touches " were 34 per cent. For the 

 animals the percentage of "touches" in the normal condition is 

 48.4 and 49 with sight eliminated. On the other hand, the " hits " 

 were 9.6 per cent, of the chances under normal conditions and 

 16.6 per cent, with the eyes covered. From these figures it is 

 apparent that the animals avoid striking objects in such a way 

 as to impede their flight much more often than they avoid brush- 

 ing against them with the tips of the wings. 



In the caves I have often seen horizontal scratches on mud 

 banks or on slime-covered walls that must have been made by 

 flying bats that were unable to completely avoid the obstacles in 

 their path. I have not seen any evidence that they ever strike 

 the walls hard enough to do themselves injury. The great agility 

 with which a bat can check its flight or change its course enables 

 it to either turn aside or take hold of an object which it strikes 

 even if it is not perceived until the animal is almost against it. 

 It is highly probable that the fatty pads which lie about the 

 nostrils have a protective value and prevent injury to the animal 

 when it strikes, head on. 



The experiments described above show that bats do not always 

 avoid obstacles in their path. Spallanzani's statement as to the 

 accuracy with which they perceive objects in their pathway, on 

 which a number of writers on natural history have based erro- 

 neous statements, are incorrect, at least in so far as they apply to 

 the species studied in the preparation of this paper. On the other 

 hand, these experiments show that bats do perceive objects that 

 they are approaching by senses other than sight or hearing as 

 usually understood. The most important sense organs for the 



