sensory adaptations of bats. 1 39 



The Species Studied. 



All of the bats found in the United States, except a few species 

 along the southern border, belong to the typical family Vesper- 

 tilionida;. In the caves of southern Indiana six species belonging 

 to four genera are found living more or less commonly. In 

 order of greatest abundance they are : The little brown bat, 

 Myotis lucifugiis ; the Georgian bat, PipisU'elhis siibflaviis ; the 

 Say bat, Myotis siibiilatiis ; the large brown bat, Eptesicus fusciis 

 ( Vespertilio fuscus of most recent authors) ; the big eared bat, 

 Corynorhimis macrotis ; and the large winged bat, Myotis velifer. 

 In the literature on the caves of this region, as well as in some 

 of the faunal papers, these species are hopelessly confused- 

 Since the vernacular name, little brown bat, is frequently applied 

 to all of the species except the big eared and large bats, it seems 

 advisable to use the equally convenient scientific names through- 

 out this paper. The observations have been made chiefly on 

 Myotis hicifugiis but also to a considerable extent on Myotis sub- 

 tilatus and Pipistrellus siibflavtis. 



These two species of Myotis differ chiefly in the size of the ears, 

 the size and shape of the tragus, and some details of cranial 

 structure and dentition. They are about the same size and have 

 the same general appearance and essentially the same habits. 

 M. lucifugus is much more abundant than siibiilatus. 



Pipistrelhis subflaznis is much smaller than the other two. It 

 differs from them in color, in the number of the teeth, the form 

 of the skull and other structural details. In habits, it is less 

 active, both in nature and in captivity. For this reason it is not 

 well suited for experiments. 



The Physical Environment. 



All the more detailed observations on bats in a state of nature 

 were made in the caves near Mitchell. Since the conditions there 

 are fairly typical of the natural environment of the animals else- 

 where, a somewhat detailed description will be giv^en. The ac- 

 companying diagram (Fig. i)will serve to illustrate the relations 

 of these caverns and openings but not their proportions. The 

 arrows indicate the direction of the stream. 



Five caves open on this tract of land, or rather there is a 



