COLOR AND THE BEHAVIOR OF ARTHROPODS 85 



was able to experiment with it while occupying a room in the 

 Marine Biological Laboratory during the summer of 1909. This 

 species is of particular interest on account of its decorating 

 habits. It takes various objects, such as bits of sea weeds, 

 hydroid colonies, or in fact, almost anything that comes in its 

 way, and sticks them on its back in such a way that it is very 

 effectually concealed among the thick growths on the piles and 

 sea bottoms. 



This crab is especially favorable for testing the question of 

 selection with reference to colored backgrounds and a series 

 of experiments was performed with this point in mind. All the 

 animals used were smaller than the adult size for the species, 

 none of them measuring more than eight centimeters in length. 

 The method employed was to clean the back of a crab with 

 a brush and then put it into a dish filled with sea water; after 

 a short time several pieces of colored papers w^ere added so that 

 a choice was offered between papers colored like the environ- 

 ment and those which were not. The dishes were cylindrical 

 in form, measuring 15.5 centimeters in diameter and seven in 

 depth; each was completely surrounded on the bottom and 

 sides by a monochrome paper. The bits of paper were of uniform 

 size (one by fifteen millimeters) throughout the experiments. 

 The behavior of the crab toward the colored papers was observed 

 from time to time for about twenty-four hours. Under such 

 circumstances, the crabs seldom failed to put some of the papers 

 on their backs, and their interesting decorative maneuvers 

 were often watched by the writer. Two kinds of experiments 

 were tried; (a) th^^se to test black vs. white discrimination, 

 and (b) those in which a variety of colors were involved. 



(a) Black vs. White Discrimination. Experiment 1 — July 6, 

 3.30 p. m., a clean Libinia was put on a black background. 

 3.35 p. M., ten pieces of black paper and ten pieces of white 

 paper were added. July 8, 11.00 a., m., no reaction to papers, 

 experiment discontinued. 



Experiment 2 — July 8, 11.25 ^^- ^^- Two Libinias were put on 

 a black background and two others on a white background; 

 11.40, twenty pieces of white and twenty pieces of black paper 

 were added to each dish. 



