REACTIONS OF CRAYFISHES. 179 



between the spaces set aside for the graphs. The previous 

 history of the animals and the gradient used with a description 

 of conditions of experimentation were entered at the top of the 

 page. After the crayfishes were dropped into the middle of the 

 tank they were disturbed as little as possible. At the end of 

 each experiment a titration of samples of water taken from 

 the two ends and center was made with sodium carbonate and 

 recorded. 



2. Stock. 



The crayfishes were of the species Cambarus propinquus Gir., 

 C. virilis Hag., C. diogenes Gir. and C. immunis Hag. They 

 were all of medium size with the exception of a few specimens of 

 C. virilis and C. diogenes which were above medium size. C. 

 propinquus and C. virilis were all taken at New Lenox, 111., from 

 the pools just above and just below the rapids and from among 

 the rocks of the rapids of Hickory Creek. The first stock was 

 obtained December 25, 1912, and was kept in the laboratory in 

 a large pan with the bottom covered with sand, gravel and some 

 vegetation. The water was changed six times per week. When 

 brought in a few died during the first three to five days, due 

 possibly to the sudden change of temperature, but after this 

 there was little mortality. Stock obtained November 15, 1912, 

 and January 25, 1913, which were kept in an aquarium, suffered 

 the same experience when transferred to the pan. Stock ob- 

 tained March 22 and 29 and June 21, 1913, was kept in an aquar- 

 ium in which was a strong flow of water to lower the temperature 

 to more nearly that of experimentation. These suffered no great 

 mortality. C. immunis was obtained from sloughs, mostly from 

 the bottom, and a few from burrows, and C. diogenes from bur- 

 rows only, along the banks of the same sloughs near Clark 

 Junction, Ind., June 20 and 24 and July 9 and 26. These were 

 all kept in large glass jars into which fresh water was flowing. 

 There was no great mortality experienced by these stocks. 



3. Habitat. 



C. propinquus is essentially a quiet water stream form. It 

 inhabits the pools with more or less muddy bottom (Williams, 

 'oi). They hide under rocks or rest quietly on the bottom. 



