I [ 8 ZOOLO GICAL SKE TCHES. 



their mates on the wing, and the Nycteris TJicba'ica even 

 carries her young on her nightly excursions. Nay, bats 

 may be said to sleep in the air, for they build neither 

 day-nests nor winter-quarters, but hang by the thumb- 

 nail, — touching their support only with the point of a 

 sharp hook. But this hand-hook connects with muscles 

 of amazing tenacity : in cold climates, where bats have 

 to club together for mutual warmth, fifty or sixty of 

 them have been found in one bundle, representing an 

 aggregate weight of about fifteen pounds, all supported 

 by one thumb-nail. The " head-centres" must sleep as 

 warm as a child in a feather bed; but it is hard to un- 

 derstand how the outsiders can survive the cold season, 

 for, in spite of its voracity, the bat accumulates no fat, 

 and the flying-membrane is a poor protection against 

 a North-American winter. The only explanation is that 

 their winter torpor is a trance, a protracted catalepsy, 

 rather than a sleep : hibernating bears and dormice get 

 wide awake at a minute's notice, but I have handled bats 

 that might have been skinned without betraying a sign 

 of life and needed more than the warmth of my hands 

 to revive them, for their wings were quite brittle with 

 rigid frost. Bats prefer a cave with tortuous ramifica- 

 tions that shelter them against direct draughts, but still 

 with a wide, though not too visible, opening, as they do 

 not like to squeeze themselves through narrow clefts. 

 A dormitory combining these requisites is sure to at- 

 tract lodgers from far and near: the northern entrance 



