SENSORY ADAPTATIONS OF BATS. 1 49 



to such an extent that the Hmbs and membranes feel cold to the 

 touch. As the animals are aroused, the breathing becomes 

 stronger, the temperature rises, the eyes open and often there 

 are convulsive movements of the limbs. The animal may also 

 begin to chatter and to creep slowly. If laid on its back it 

 slowly rights itself However, it is some time before it gains full 

 control over its muscles. If dropped, the wings spread reflexly, 

 but the animal cannot at once fly. There are intermediate stages 

 of lethargy in which the torpor is less extreme and the animal 

 very quickly gains power over its body, but the extreme condi- 

 tions described above have been observed in every month of the 

 year except May, June and July, during which months but few 

 bats have been under observation. 



Observations on periodic movements of bats were made chiefly 

 at two points in the caves at Mitchell, in the large chamber 

 (Fig. I, 2) at the right of Shawnee Cave, and at a point about 

 100 feet within the Twin Cave entrance (5). Both points are so 

 near the entrance that the temperature varies considerably. On 

 bright days a diffuse light reaches both points for an hour or 

 more when the sun's rays fall directly into the mouth of the 

 cave. Daily observations were recorded from January to April, 

 1907, with the exception of several times when high water pre- 

 vented entering the cave. 



On January 2, with a maximum temperature of 50° F., there 

 were 75 bats at the place of observation in the Twin Cave. A 

 period of low temperature followed, and high water prevented 

 further observations until January 25, when the number had 

 decreased to 9. The number now increased gradually until 

 February 7, when there were 51, although the temperature 

 remained low. With the average temperature slightly rising, 

 the number of bats diminished during the next two weeks to 42 

 on the twenty-first of the same month. During the next four 

 weeks the number of bats again increased until on March 20 

 there were loi. The temperature had been rising gradually and 

 with some fluctuations, and the average daily temperature on 

 March 20 was about 45°; a further rise to 70° on March 27 

 followed. With these higher temperatures the number of bats 

 on the twenty-eighth of that month was only 18. Unseasonably 



