HARRIS : CRAYFISHES GENUS CAMBARUS. 91 



furnish food, but when these become parched and dry, they 

 must either dig after and eat the roots, or search in the stream." 



Abbott ('84) does not agree with Tarr's ('84) conclusion that 

 the "chimney" is simply the rejected material, but thinks that 

 it is the product of design on the part of the animal, which 

 "often studies the localities with care, and builds to suit the 

 chosen site." His reasons for the conclusion are that on the 

 sloping side of a ditch, where, had the material been simply 

 rejected, it would have rolled down the bank, artistic towers 

 two inches in diameter and from eight to eleven inches in 

 height were erected. "In several instances the base of the 

 tower was especially prepared for by having the ground leveled 

 and smoothed before the foundation masses of puddled clay 

 were put in position. Of a series of forty towers built by the 

 Camharus diogenes that I observed on the banks of a ditch, not 

 one could have been the result of accident, as suggested by 

 Mr. Tarr." 



"The towers that were found in meadows at a considerable 

 distance from open water were invariably broader at the base 

 and never so high as those described on the edge of flowing 

 water. These open-meadow towers or chimneys, however, 

 were all found to be composed of pellets of clay so arranged as 

 to render it highly improbable that their positions were fortui- 

 tous. Indeed, in the majority of instances it would have been 

 practicable to have rolled the little balls of clay to a consider- 

 able distance from the opening of the tunnel." 



Mr. Abbott suggests that the fact that some of the most 

 elaborate structures are the result of the work of half-grown 

 or even smaller crayfish may have a bearing on the question of 

 design in "tower" building. "Some of the most slender and 

 tallest were the work of diminutive little fellows, who certainly 

 could have avoided a deal of labor if the chimneys or towers 

 were not designed." 



Abbott ('85) gives the results of the observations of his 

 nephew, Mr. Jos. DeB. Abbott, who, by the aid of a candle, 

 observed the crayfish building his "chimney." According to 

 him, the crayfish was seen to partially emerge from its burrow, 

 bearing "on the back of its right claw a ball of clay mud which, 

 by a dextrous tilt of the claw, was placed on the rim of the 

 chimney. Then the crayfish remained perfectly still for a few 



