96 Journal New York Entomological Society. [Vol. xm 



less powerful stimuli, such, for example, as differently colored back- 

 grounds in place of strongly contrasted ones; and that underlying 

 these quick and slow reactions of the chromatophores to changes of 

 environment, there was at least one intrinsic chromatophoric rhythm, 

 the after effect of alternating night and day." 



They confirm the view that light sets up movements of the pigments 

 by its direct action on the chromatophores. " Light exerts a potent 

 and varied influence on the littoral Crustacea. Such animals as Hip- 

 polyte, Mysis, and Palcemon, instead of becoming inured, remain 

 highly susceptible to the ever-changing light conditions of their en- 

 vironment." It also plays an important part in controlling not only 

 the movements of these animals, but also the distribution of their 

 pigments. The factors in pigment-movements are intensity, back- 

 ground or environment, and monochromatic light. 



The color-phases in shrimps depend on different light conditions. 

 In darkness the pigments of Paicemon, etc., are so contracted into 

 their chromatophore-centers, that the latter appear as minute dots, 

 resulting in a transparent phase. The rapidity with which the change 

 takes place varies from ten or a less number of minutes to an hour 

 or two. 



What the authors call the "white background phase," /. e:, a 

 transparent condition, the pigments being freely contracted, may be 

 and generally is assumed with great rapidity, less than a minute often 

 sufficing to call it forth in Hippolyte or Macromysis flexitosa. Here 

 we might add that Pouchet found that in the turbot under certain 

 conditions the color changes are only developed after a period of 

 several days. Very pertinent to the matter of change of color in 

 spiders and insects are the author's conclusions as to the environ- 

 mental or background effects on littoral Crustacea. " The background 

 effects on pigment-movements, help us," they say, "to imagine how 

 light modifies pigment-development and thus causes such an animal 

 as Hippolyte to ' give into ' its surroundings, modelling its diurnal 

 pigment distribution on the distribution of light and shade on its 

 background." They add : "As long as its background is unchanged, 

 change of intensity avails little. Now of all things which charac- 

 terize Hippolyte its tenacious immobility on the weed of its choice is 

 the most striking." 



