SENSORY ADAPTATIONS OF BATS. 1 67 



the first row, but they were high in the comb of the roof, the bats 

 seldom passed between them, and as they had no apparent effect 

 upon the experiments they will be counted as though all were in 

 one series. 



Wires were used in these experiments in preference to larger 

 objects because a bat will invariably try to perch on any object 

 it strikes and it is sometimes difficult to tell whether the animal 

 intended to perch or whether it did not perceive the object. 

 Wires have an advantage over strings because the slightest touch 

 causes a perceptible sound and it is not always easy to see whether 

 an object is touched. Some preliminary experiments were made 

 in April but the method of quantitative study was not decided 

 upon until May 16, when one bat was used. Several more were 

 tried during May and June but at this time few bats were in the 

 cave. The experiments were therefore discontinued until later 

 and most of them were made between August 25 and Septem- 

 ber 5. 



Some of the animals were very fat and inactive during late 

 summer and it was difficult to keep them flying. There are great 

 individual differences and some of the experiments required six 

 times as long as others and some bats had to be discarded for 

 the purpose of these experiments because they would not fly at 

 all or would make short flights in one corner of the room and 

 not attempt to pass between the wires. The tabulated results 

 were obtained from the use of 48 bats belonging to three species. 

 About fifteen additional individuals and two additional species 

 were liberated in the experiment room but are omitted from the 

 tables because the data are incomplete. The total numiber of 

 observations on avoidance is about 6,000. 



The individual differences and the varying degrees of lethargy 

 in the same individual at different times make it essential to deter- 

 mine the normal reactions of each animal before trying experi- 

 ments under changed conditions. For this reason it was deemed 

 necessary to test each individual in a normal and uninjured con- 

 dition immediately before the experiment in which one of the 

 senses was impaired. 



Tiie bats were captured in the cave and were generally used 

 for the experiment on the same day, although some of them were 



