Temporary Tenants of Caves.— In modern times, as anciently, bears and other carnivores use caves as sleeping-places when it is con venient, but they are exclusively resorted to by a few kinds of creatures that may properly be called cave-tenants. The most characteristic of these probably are certain bats, especially such insect-eating kinds as the leaf-nosed, the horse shoe and the true bats of the family Vesper tilionidse. Caves frequented by bats usually harbor enormous colonies, and one who enters and disturbs them will find himself in the midst of a whirring multitude that it taxes the powers of description to portray. Some caves long occupied contain vast deposits of the rich est possible guano, and this has been extensively utilized in some places as a fertilizer. Such artificial caverns as the deserted tombs of Egypt are filled with bats, one species of which is popularly called tomb-bat, and abounds in the interior of the Great Pyramid.
Birds of two sorts are cave-tenants. The most singular, probably, is the large guacharo, or oil-bird, of the family Steatornithida, classi fied between the nightjars and the owls, and inhabiting northern South America and the island of Trinidad. It inhabits both sea-side and mountain caverns, going forth only at dusk to get its food, which is mainly fruit. "Visitors to the breeding-caves," says Evans (Birds,' 1900) "are suddenly surrounded by a circling crowd of oil-birds uttering loud croaking or rasping cries. . . . The numerous nests . . are flat, circular masses of a clay-like substance placed on ledges or in holes." Great numbers of these birds are killed by torch-light for the sake of the oil obtained from them, which is excellent for illumination or for cooking pur poses. The other birds choosing sea-caves as a breeding-place are swifts of the genus Collo calla, whose nests are placed in the depths of caves on the coasts of Ceylon, and eastward and southward to northern Australia. The best known of the many species is that which pro duces the edible nest of which the Chinese are so fond. Huge numbers of these swifts breed in company in dark caves, where they are asso ciated with bats; but the bats go outside at night and the swifts by day. Such caves con tain. exceedingly rich deposits of guano, and return to their owners a large rental for the right to gather the swifts' nests glued to their walls and roofs. See Swims.
Blind Inhabitants.— A special cave-fauna exists in all parts of the world, consisting of an assemblage of animals of different classes which are blind, and in most cases eyeless. This fauna is evidently of great antiquity, since it exists most plentifully in caves, such as those of the limestone district of the South-Alle ghanian region, and in southern Europe, which regions are south of the region of the Pleisto cene glaciation. Within such caves, formed by
the action of water (see Cava), are rivers, sink holes and deep wells, all perfectly dark, in habited by blind amphibians, fish, crayfish and other crustaceans, and by many kinds of in sects and spiders. No vegetation exists save a few scattered molds and fungi, and all the animals are carnivorous, preying on each other. Mammoth Cave in Kentucky contains about 75 species of these blind creatures, to which 40 or 50 more may be added from other south ern caves; while several hundred kinds have been described from European caverns.
The most striking and interesting form in Mammoth Cave is the blind-fish (Amblyopsis spekeus). It is about four inches long, color less and blind, the eyes being vestigial. This fish seeks the dark and shuns the light, being much disturbed by a lighted match or bright sunlight, or even by a ray of light. In well-fed adult specimens there is no external indication of an eye; but in young ones, before reaching a length of two inches, the eyes can be distinctly seen, owing to their pigment, which is lost in the adult. The optic nerve can be traced in examples under an inch in length. This will apply to the eyes of other blind fishes and blind insects, crustacea, etc. While the sense of sight is lost, that of touch in the blind-fish as in most other cave animals, is exalted. Amblyopsis 'is provided with tactile papillae, arranged in ridges on the front and sides of the head. They are said to show extreme timidity and caution in their movements.
A still higher type of vertebrate, two species of salamanders, have become adapted to cave life, losing their eyesight by disuse. The species of the genus Spelerpes frequent damp, dark situations and the entrances to caves. An allied form (Typhlotriton spekeus) is distinctly a cavernicolous as distinguished from a twilight species, and has never been found outside of caves. Its eyes show early stages of degenera tion. It inhabits caves in southwestern Mis souri, and occurs under rocks in and out of water. Still another salamander, whose eyes are the most degenerate known among am phibians, is the Typhlomolge rathbuni. It lives in subterranean streams, tapped by an artesian and also a surface well, near San Marcos, Tex., and in one of the caves near that town. Its remarkably long and slender legs are too weak to support its body when out of water.