The lower animals tell the same story of de generation, total or partial atrophy of the eye, together with loss of color, and, in a more striking way, the compensation for the loss of vision by a great increase in length of the antenna and other appendages, or by the growth of long, slender tactile bristles.
The blind crayfish (Oreonectes pellucidsos) is a common cave form. It differs from its out-of-door allies in being blind, deaf, slender bodied and colorless. Other blind or eyeless crustaceans are various kinds of amphipods and isopods, both aquatic and terrestrial, of which species of Ctecsdotea are the most abundant, and form the food-supplv of the blind crayfish.
The eyeless beetles of caves (Anophthalmi) have no vestige of eye or of optic nerves, while their bodies and appendages are slender. They grope their way about by means of very long tactile bristles. Other beetles, such as Adelops, which have retained vestiges of the outer eye; some spiders comprising an eyeless species, and others with eyes varying in size, some much reduced, spin little webs on the walls of the chambers. Among the harvestmen some (Pha langides) have extraordinarily long legs; while the Campodea (q.v.), a wingless insect
of the Mammoth and other caves of the United States and Europe, differs from the outdoor form in its antenna and abdominal appendages, being greatly exaggerated in length. There are also mites, myriapods, primitive wingless insects (Podurans), a few flies, worms and infusorians.
Origin and The blind fauna of caves, according to Packard, is composed of the descendants of individuals which have been carried by various means into the subterranean passages, have become adapted to life in per petual darkness, becoming isolated, and thus, as long as They are subjected to their peculiar environment, breed true to their species, and show no tendency to relapse to their originally eyed condition. The absence of the stimulus of light causes the eyes, through disuse, to under go reduction and atrophy.' With this goes, in certain forms, the loss of the optic ganglia and optic nerves.
Packard, A. S., 'Cave Fauna of North America' (Washington 1:-:;) ; Eigeman, C. H., Vertebrates of America' (Washington 1909) ; (Land Mammals of Western Hemisphere' (New York 1913) ; Morgan, T. H., and Adaptation' (New York 1903).