THE MAMMOTH CAVE OF KENTUCKY. 6^ 



can return^, but by no means so pleasant as the paddle down the 

 river : it is through a slippery, disagreeable place called " Purgatory." 

 It sometimes happens that the[flow of water from Green River is 

 a few degrees warmer than that of the Echo River water^ and a 

 fog is the result. In the Echo River most of the eyeless fish are 

 caught. They afford [a striking instance of the non-developement 

 of organs not used. Their ancestors must have come into the 

 cave, but there being no light there was no use for the organs of 

 vision 3 and, hence, in the present natives of the cave- waters the 

 eyes are undeveloped. There is another class of fish in which 

 there is an internal eye, which can only be distinguished after 

 removing the skin. In the first class the entirely eyeless ones are 

 quite white, but those with internal eyes are a whitish brown, — the 

 natural result of the absence of light. This fact is a substantial 

 proof of the correctness of the theory accounting for the existence 

 of the eyeless fish. It seems to indicate that |with the whitish 

 brown the process is still going on, and that their ancestors have 

 not been so long in the cave as those from which the white eyeless 

 fish have descended. They are never more than eight inches long, 

 and live only a few weeks when taken from the cave. Whether 

 this is owing to starvation or exposure to the light is not known. 

 At the Mammoth Cave Hotel were two fish in a small glass 

 vessel, which had been there for six weeks : this was the longest 

 time any of these creatures had been kept alive. The only thing 

 done was to change the water, as attempts to give them food had 

 caused death. They probably live on the Infusoria they find on 

 the water, and the larger may live on the smaller. When the 

 white ones are placed in clear water, and the sun shines, they are 

 semi-transparent. A species of craw-fish are also found in the 

 cave, and no trace of an eye has been discovered in any of the 

 specimens examined. 



We landed at Silliman's Avenue, so named after Professor 

 Silliman, who visited the cav^e some years ago. It is a fine avenue, 

 li miles long, twenty-five to forty feet in height, and in parts two 

 hundred feet wide. It is full of interesting curiosities, but I have only 



