LITUOBIUS 93 



indicating an acute sense of hearing. These peculiarities 

 are special adaptations to a nocturnal life in which other 

 senses replace that of sight. During the daytime bats lie 

 hidden in hollow treses, crevices of rocivs, in caves, and behind 

 window blinds of liouses. Tittle explanation can be given 

 for their peculiar relation to light ; it does not seem to be an 

 adaptation to feeding on nocturnal animals, for many bats 

 are frugivorous. Doubtless they gain from their nocturnal 

 habits a certain immunity from attack by hawks and other 

 birds of prey. The most primitive of the living bats fly late 

 in the day. As the group evolved the hal:)it of flying at night 

 was subsequentl}' acquired, and this suggests that bats have 

 been getting more and more sensitive to light. In caves, bats 

 fly back and forth but pass often into the free air to capture 

 flying insects. Then, before dawn breaks, they return to the 

 darkness of the cave. 



The commonest salamander that inhabits our caves belongs 

 to the species Spelerpes maculicaudus. This genus is wide- 

 spread, being known from New England to Minnesota and 

 into the Southern States. In New England, where there are no 

 caves, it lives among the rocks and, like its relatives of the 

 same genus, prefers moist crevices and lies concealed during 

 the day. Wherever there are caves, as in Indiana and Ken- 

 tucky, this salamander is found inhabiting them in great num- 

 bers, just because the caves offer the conditions to which they 

 are adapted. The eyes of this salamander are functional, but 

 there are other, less common, cave salamanders whose eyes 

 arc degenerating. 



The cave fishes of the United States all belong to one family.* 

 Those members of the family that live in caves have a 



1 The Amblyop'sidfE (Fig. 95 o). 



