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. 



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