Amblyopsis

Amblyopsis, a North American bony fish, found in the Mammoth Cave of Kentucky, and interesting as illustrating in the rudimentary condition of its eyes the effects of darkness and consequent disuse. It only measures a few inches in length, is colourless, and has its small eyes covered by the skin. It seems able, however, to hear acutely, and the wrinkles of skin on its head are regarded as special feeling organs. Typhlichthys is a closely allied genus found in the same surroundings, while another relative, Chologaster, occurring in the ditches of the South Carolina rice-fields, is, as one would expect, open-eyed. The caves are tenanted by similar half-blind animals of various classes (see PROTEUS, and CAVE-ANIMALS). Truly blind fishes are only found in the unsunned ocean depths.