Popular Science Monthly/Volume 46/April 1895/Animals That Live in Caves
|ANIMALS THAT LIVE IN CAVES.|
By E. A. MARTEL.
THE study of paleontology and prehistoric archæology and the exhumation of the life of the past in caverns have been pursued in France during the last twenty years at the expense of the investigation of the present life, while the fauna and flora of their black recesses and dark waters have nevertheless flourished quite as vigorously as in the subsoils of Austria and America. The naturalists of those countries have, however, carried their investigations in that domain considerably further than those of France, Still, numerous cave-dwelling species new to us have been found in the Pyrenees and the south and east of France.
The zoölogical study of subterranean waters is eminently useful to hygienists, to whom it discloses the presence of noxious organisms capable of developing in the water supplies of cities, and thence finding their way into the human economy.
Animals of all classes may be found in caverns. Some, which do not pass all their existence there, but seek shelter in them, have been called by the Austrian Schiner troglophiles (or cave lovers), and others, which never leave their dark abodes, are designated by him as troglobiens (or cave dwellers). I can not present here even a simple picture of the subterranean fauna actually known; I can hardly even sketch the outlines of the subject and insist on its importance.
The higher vertebrates—mammals, birds, and reptiles—found in caves seem to be chiefly troglophiles. There are, however, real troglobiens among the lower vertebrates—batrachians and fishes. The articulates, in particular, and especially the arthropods—insects, myriapods, arachnids, and crustaceans have revealed many species previously unknown. The Dolichopoda palpata, represented in the figure, was discovered by M. E. Simon, in 1879, in the grottoes of Belves and Espezel, in the Aube. Worms, mollusks, etc., are not rare.
The list of the fauna of the Mammoth Cave in Kentucky comprises no less than a hundred species, without counting those that come in casually from without. Blind spiders set their nets for eyeless flies. Fish eat crawfish, which feed upon smaller crustaceans pulled with their pincers from beneath the flat rocks, while the crustaceans prey upon defenseless mollusks, and these forage upon microscopic fungi.
The important question of the origin of the subterranean fauna is still invested with a degree of mystery. It was at one time believed and maintained by Agassiz that they were specially created for the medium in which they live. It was afterward recognized that they are derived from species that have simply undergone external modification. A careful comparative study of the modifications they have undergone, and of their phases, would be necessary to clear up the doubtful points. The doctrine of the evolution of species is concerned in this investigation. The introduction underground of the ancestors of these fauna may have taken place and may be taking place in two ways: through perfect individuals carried by streams into wide-mouth pits, whence they can not escape to the light, or through eggs or larvae borne into narrow fissures by simple infiltration of water. It is a matter of question whether or not creatures hatched from these germs, which have never lived on the surface, and their descendants,
Blind Insect of Caves (Dolichopoda palpata).
would be affected by more rapid changes than those which have come underground by accident, but have not been born there. The principal changes undergone are usually albinism, or more or less complete loss of color, and atrophy of the eyes. The organs of vision become, of course, useless in the underground darkness. It is found, on the other hand, that cave-inhabiting animals have the other senses developed to excess; they guide themselves by means of long cirri or long antennae, which are very sensitive; they are put on their guard by means of their hearing, which informs them of distant perils; and by their smell, telling them of invisible game, helps them to their food. Albinism is accounted for as the result of failure to absorb the light-rays. It is generally agreed that cave-dwelling animals have lost through adaptation to the medium the visual organ their ancestors enjoyed.
Schioldte, of Copenhagen, and Dr. Gustave Joseph, of Breslau, have made curious studies of the transitions in gradual atrophy of vision from aërial animals to their cave-inhabiting congeners. M. Joseph believes that when the light is diminished in the animal's habitat, dislocation of the eyes takes place, and that the intermediate species are especially domiciled in caves where a twilight prevails, or where a little light enters at noon or in summer. While the Proteus and the Amblyopsis of the Mammoth Cave have the eyes simply covered by a membrane, some mollusks appear not to have even a place for the most rudimentary ocular globe. We might, however, ask if these different degrees of blindness do not proceed in a measure from differences in the length of time that has elapsed since the species were buried. On the one side, some animals have been found in caves having their eyes preserved in full vigor; on the other side, artesian wells have thrown to the surface, and some subterranean lakes have yielded to the collector, living beings in no wise modified from those living above ground. It has been reasonably concluded from this that these beings have been drawn in by the water that feeds the lakes coming from unknown distant points, and that their abode underground has not been long enough continued to make them blind. It would be interesting to compare atrophy of vision in cave-inhabiting animals or in those of subterranean waters with those remarkable creatures specially adapted to enormous sea depths which, have been collected in the expeditions of the Challenger, Talisman, and others of like purpose.
It is perhaps possible to attach too much importance to the blindness of subterranean animals as a peculiarity. A considerable number of species living in surface waters are destitute of vision.
M. Joseph is of the opinion that "the presence or absence of organs of vision always corresponds with the conditions of existence of the animals." So far as concerns the heredity of atrophies, Hovey says, in his Celebrated American Caverns, that Dr. Hayden witnessed the birth of eight little blind amblyopses.
What we have said is only the present indication of some of the questions raised by underground zoölogy. An ample harvest of facts heretofore not observed may be anticipated from the exploration of the numerous caves of the Causses in France—such as have been made in the caves of Carniola and the United States—or of any caves as yet virgin to scientific examination. The subject is full of interest, and all the more attractive because so much still remains to be found out about it.
The outfit for hunting cave-inhabiting animals includes an entomologist's pincers, a fine, strong, close-meshed net, a brush for applying alcohol to the creatures to stupefy them, and vials or bottles of different sizes and shapes for holding the collections, either dry or in spirit. Of special importance are practical experiments on the physical modifications which animals of the outer world may undergo when shut up for a long time in the depths of caverns.—Translated for The Popular Science Monthly from La Nature.
- R. Moniez, Faune des Eaux souterraines.