82 



A. S. PEARSE 



SO that they more nearly corresponded to their environment. 

 The dark median stripe down the abdomen was more prominent 

 in those individuals kept in the red and black boxes; those in 

 the blue had a decided bluish tint ; and those in the yellow were 

 noticeably yellowish. Control animals of similar size and age, 

 kept in open glass dishes did not show such variations. These 

 results agree with those of Kent ('oi) who made similar experi- 

 ments on a related species of the same genus of crayfishes. Such 

 color changes are apparently not uncommon among crustaceans 

 and many more striking examples might be cited. 



After the craA^fishes had been kept for seme time in the color 

 boxes the next step was to ascertain whether such prolonged 

 subjection to a monochrome environment would cause them 



L 



WINDOW 



3LAC K 



Figure 2 — Ground plan of apparatus for testing the reactions of the crayfish to 

 colors. A, runway where animals were placed; b, b', c, c', remo^'able 

 colored cardboards. 



to move more often toward one color than another. This was 

 tested by means of the apparatus shown in Fgure 2. It con- 

 sisted of a rectangular glass dish (10 cm. high, 40 cm. long and 

 24.5 cm. wide) fitted up so that an animal could be placed 

 at the beginning of the runway, A, and allowed to move down 

 it until it must choose between the two sides b and b'. The 

 only difference between these sides was in the colored screens 

 c, c' and the cardboards b, b' which could be changed at will. 

 The glass dish was filled with filtered water to a depth of four 

 centimeters during the experiments, and the whole apparatus 



