306 VICTOR E. SHELFORD. 



Calopteryx does not react sharply to bottom in these tests as 

 it clings in vegetation particularly in sand bottomed pools but is 

 frequently found on sand bottom. 



Campeloma, Macromia, Anodontoides, and Sphcerium. After 

 creeping about for some time in the unnatural conditions of the 

 experiment, come to rest, burrow in the sand, in most cases with a 

 small portion of the body protruding. Sph cerium burrows well 

 only in the presence of a current. 



3. TYPICAL RESULTS. 



In the rapids community we note that there is a striking avoid- 

 ance of sand by the animals living below the stones; less striking 

 by those living on and among the stones. There is then a general 

 agreement in the preference for hard surface and avoidance of 

 sand. The animals of the pools all show a large preference for 

 sand especially those living on the bottom; Calopteryx in the 

 preliminary experiments showed no preference for either end but 

 is for some reason commonly associated with sand. Since the 

 fishes did not react to bottom in such small space it was necessary 

 to draw, by way of predicting the character of response, data 

 calculated from collections by Forbes and Richardson ('08). 

 Here relations to mud and sand and rock are not clearly separated 

 but the preference clearly includes sand for the majority of 

 cases. The data in Fig. 34 shows the extent to which the 

 tabulated animals burrow. 



4. REACTIONS TO STONES. 



The reactions of the animals to stones were tested in the 

 apparatus described for the bottom experiments. Two pans 

 with waxed bottoms were placed side by side under the hood. 

 In one half of one was placed a number of irregular pieces of 

 quartz 1X2 inches and a number of pieces about % of an inch in 

 diameter. Ten individuals of each rapids species were placed 

 in each pan and left in entire darkness. A one candle power 

 lamp was turned on for the readings. The percentage of animals 

 found under, on and among stones is shown in Fig. 33. The 

 preference for stones was strong. Only the darters, crayfishes 

 and Argia showed an avoidance of the stones in 20 per cent, or 



