COLOR AND THE BEHAVIOR OF ARTHROPODS 105 



to attempt to discover just what factors are responsible for a 

 preponderance of yellow Misumenas on yellow flowers and of 

 white individuals on white flowers. The writer has some evidence 

 that such distribution may be due to the attacks of predaceous 

 enemies, but it is not conclusive, and he rests his case here 

 without attempting to discuss this or other factors. Whatever 

 the cause of the general correspondence between Misumena and 

 the colors in its environment, it is not due to color change nor 

 positive chromotropism. 



GENERAL CONSIDERATIONS 



Coloration of Arthropods. Arthropods are sharply separated 

 from all other groups of invertebrate animals; nevertheless, 

 they possess certain common structural similarities which indi- 

 cate a genetic relationship among the members of the different 

 classes. There is great diversity among the different groups 

 of arthropods, not only in structure but also in habits, and, if 

 w^e compare the four chief classes, coloration is not by any means 

 the least variable feature. 



The colors of Crustacea depend primarily upon chromatophore 

 systems (Keeble and Gamble, 'oo, '04; Frohlich, '10; Franz, '10). 

 These are usually deep seated and there is a migration of pig- 

 ment granules in them to bring about more or less striking color 

 changes which make the animals resemble their environment 

 with varying degrees of accuracy (Beebe, '09; Keeble and 

 Gamble, '00; Kent, '01). In many crustaceans the color phases 

 are strongly periodic, appearing alternatingly with day and 

 night, (Keeble and Gamble, '00), but the color changes are, 

 nevertheless, chiefly induced by the presence or absence of light 

 together with the tint of the background (Keeble and Gamble, 

 '00; Kent, '01; Frohlich, '10; Franz, '10). The color changes 

 of some crustaceans are apparently controlled in part by the 

 nervous system, but there is no doubt that, even in such cases, 

 changes may be brought about by the direct effect of light on the 

 chromophores (Keeble and Gamble, '00; Frohlich, '10). 



The colors of Myriapods have not been studied, to the knowl- 

 edge of the writer, and they are comparatively uninteresting, 

 for the color of many species appears to be mostly in the chiti- 

 nous exoskeletal covering. 



Spiders, the most common arachnids, present a great diversity 



