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 rudimentary as those of a mole, or of the strange fishes that were discharged 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 persons 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 Thebaïca 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 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 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-Höhle in the Hartz are tenanted by hundreds of thousands of bats that avoid all the neighboring cav-
