59 8 THE POPULAR SCIENCE MONTHLY. 



light as miracle-mongers dread the light of science ; but they all have 

 the exaggerated optics of an owl, evening-eyes, that catch every ray 

 of the fading twilight, while the eyes of the bat proper are as rudi- 

 mentary as those of a mole, or of the strange fishes that were dis- 

 charged from the subterranean tarns of Mount Cotopaxi. 



As the Euclidean punctum is defined as a point without extension, 

 the voice of a bat might be called a sound without vibrations a 

 shrill, sudden squeak, unlike any other sound in nature or art. Though 

 piercing enough to be heard from afar, it is too abrupt to guide the 

 ear in any special direction ; you can put a wood-bat in a narrow 

 box, and the box on the table, and bet large odds that the incessant 

 shrieks of the captive will not betray its hiding-place ; to nine per- 

 sons out of ten the sound will seem to come from all parts of the room 

 at once. 



Many of their habits, too, distinguish the cheiropters from all 

 other creatures of our planet. Aristotle classed them with the birds ; 

 and in one respect they might even be considered the representatives 

 of the class, being par excellence creatures of the air. All winged 

 insects can run or hop ; the sea-gull runs, swims, and dives ; but, with 

 the sole exception of the Javanese roussette, bats are completely " at 

 sea" in the water, and almost helpless on terra firma ; they eat, drink, 

 and court their mates on the wing, and the Nycteris Thebalca 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-centers" must sleep as 

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

 tection 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 ramifications 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 

 attract lodgers from far and near ; the northern entrance of the tunnel- 

 grotto of Posilippo and the Biels-Hohle in the Hartz are tenanted 

 by hundreds of thousands of bats that avoid all the neighboring cav- 



