136 GENERAL ZOOLOGY 



in summer and burrow into the earth until they come to 

 water. At the bottom of their burrows, sometimes three feet 

 from the surface, they dig out a flask-shaped enlargement 

 and stay in it or near it till the next spring. The chimneys 

 made at the top of the " wells," referred to in the quotation 

 at the beginning of the chapter, are made by the burrowing 

 crayfish merely as an incident in getting rid of the mud 

 brought from below. Sometimes crayfishes stop up their bur- 

 rows completely. In that case they probably remain in a 

 dormant condition without food till spring returns. In the 

 bed of a pond or river where jutting stones abound cray- 

 fishes rest with the abdomen doubled beneath them and the 

 head toward the open. Boys often lure them from their 

 hiding-places with a piece of meat tied to the end of a 

 weighted string. The animal invariably seizes the meat in 

 a cheliped, and usually can be drawn to the surface before it 

 has time to " think " the matter over and let go. 



The distribution of crayfishes is directly related to their 

 power of adapting themselves to conditions of considerable 

 variability. If a certain definite degree of temperature or of 

 clearness of water were required, they would be restricted to 

 a very limited area, and, indeed, it would be difficult for 

 them to maintain themselves at all. As it is, we find them 

 in drinkable water, in muddy water, in sulphur-laden water, 

 and in sea-water, but never in the water of streams or ponds 

 of a country devoid of limestone. This accounts for their 

 absence from the eastern part of New England, where the 

 rocks are largely of granite. 



A striking example of adaptation to an unusual environ- 

 ment is found in the cave-dwelling crayfish, Oambarus pel- 

 lu'cidus. Professor Eigenmann of Indiana, Dr. O. P. Hay 

 of New York, and others have explored the caves of Indiana 

 and Kentucky for the purpose of studying the animals of 

 their subterranean rivers. The blind crayfish has small and 



