80 A. S. PEARSE 



are beneficial to the animals possessing them, and it is quite 

 generally believed at present that "natural selection has un- 

 doubtedl}^ been the chief factor" (Kellogg, '05, p. 613) in de- 

 veloping most of the striking cases that have been recorded. 

 Not only have the colors of numerous animals been shown to 

 correspond very closely to those found in their natural environ- 

 ment, but many species are known to change their colors under 

 certain conditions in a very striking manner, thus causing them 

 to harmonize very closely with the background. 



Notwithstanding the amount of evidence which has been 

 accumulated along these lines, little attention has been given 

 to the reactions of protectively colored animals with respect 

 to their color environment. The experiments described in this 

 paper were undertaken to determine, if possible, whether the 

 reactions of arthropods to colored backgrounds and colored 

 objects are such as to bring them into the best surroundings; 

 in other words, do the reactions of protectively colored arthro- 

 pods indicate that such animals realize that their coloration 

 is advantageous on certain backgrounds, but not on others. 

 No attempt was made to demonstrate color vision in these ex- 

 periments, i. e., the perception of colors per se. The following 

 animals were studied : A crayfish, Cambartts propinquus Girard ; 

 a caddis fly larva, said by Professor Charles T. Vorhies to belong 

 to the genus Neuronia and probably to the species postica Walker ; 

 a spider crab, Lihinia emarginata Leach; and a spider, Mis- 

 umena aleatoria (Hentz) Emerton. The original experiments 

 with these animals will first be considered and all general ques- 

 tions left for discussion later. 



DESCRIPTION OF EXPERIMENTS 



The Crayfish, Cambarus propinquus Girard. — In order to 

 ascertain the effect of subjecting crayfishes to various color 

 environments for long periods of time, twelve individuals were 

 selected which were as nearly alike in color and size as possible 

 (56 to 66 mm. in length); half of these were males and half 

 females. Owing to the fact that two of the females died after' 

 the experiments were begun, only the males were used in testing 

 reactions. 



A pair of crayfishes was placed in each of the six rectang- 

 ular glass jars used for the experiments. These jars measured 



