THE CRAYFISH 155 



ing themselves in crevices or under protecting pieces of 

 rock or submerged logs. Several species make burrows in 

 the soft earth of meadows. The most widely distributed of 

 these is Cambarus diogenes. Species which live in ponds 

 that are likely to dry up in the summer, and also a few that 

 live in rivers, leave the water 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 burrows 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 crayfishes 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' 3 

 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. 



A striking example of adaptation to an unusual environ- 

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

 lu'cidus. Professor Eigenmann, Dr. 0. P. Hay, and others 

 have explored the caves of Indiana and Kentucky for 

 the purpose of studying the animals of their subterranean 



