THE BLINDNESS OF THE CAVE FAUNA AND THE ARTIFICIAL PRODUCTION OF BLIND FISH EMBRYOS BY HETEROGENEOUS HY-BRIDIZATION AND BY LOW TEMPERATURES. 1 (WITH 13 FIGURES.) JACQUES LOEB. I. While many of the animals inhabiting caves are blind or have degenerated eyes, the same phenomenon is rarely found among animals that live in the open. At first sight this seems to suggest that the disuse of the eyes in the complete darkness of the cave has gradually led to the degeneration of the eyes and this idea seems at one time to have been widely accepted. In forming a judgment of the connection between the darkness of the caves and the blindness of cave dwellers we must remember that some of the cave dwellers have perfectly normal eyes. Thus Eigen-mann, to w T hom we owe the most thorough study of this subject, points out that of the four species of salamanders living habitually in North American caves two have apparently quite normal eyes. They are Spelerpes maculicauda and Spelerpes stejnegeri. Two others living in caves have quite degenerate eyes, Typhlotriton spelcEus and Typhlomolge rathbuni. 2 If disuse is the direct cause of blindness we must inquire why Spelerpes is not blind. Another difficulty arises from the fact that a blind fish, Typhlogobius, is found in the open (on the coast of southern California) in shallow water, where it lives under rocks in holes occupied by shrimps. One must again ask the question: How can it happen that in spite of the exposure to light Typhlogobius is blind? The most important fact is perhaps the one found by Eigen-1 From the Rockefeller Institute for Medical Research, New York. 2 Eigenmann, "Cave Vertebrates of America," Carnegie Institution Publica-tions, Washington, 1909. 50
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