710 William Patten 



taut, but they then have a simple, protective function, as we hope to 

 show later. 



Thepigment found deposited in the cells of the lower animals, such 

 as Protozoa, Coelenterates and Crustacea, cannot be a merely protec- 

 tive coloriug, for in innumerable cases it has just the reverse effect. 

 Among pelagic animals, otherwise perfectly transparent, regularly 

 distributed chromatophores containing red, browu, or black pigment 

 are widely present. These chromatophores , aecording to the theory 

 that pelagic animals are transparent in order to escape notice, must be 

 a decided disadvantage. They are highly sensitive to changes in the 

 amount of light. Mayer (83) has shown that the chromatophores of 

 Crustacea are not only sensitive to the amount of light, but are 

 under the control of the will. This faet is of interest, since we must 

 suppose that, originally, the action of the chromatophores was involun- 

 tary and dependent upon Irritation from without. I have myself 

 observed the slow modifications in the shape of the beautifully star- 

 shaped chromatophores of Beroe ovata, produced by changes in the in- 

 tensity of the light. 



It is well known that pigmeut, like Chlorophyll, is dependent for 

 its existence upon the sunlight; animals living in absolute darkness, 

 as in caves, being colorless. It is very probable that the color of 

 animals depends upon the color of the light they receive, those receiv- 

 ing sunlight directly, without reflection, showing a tendency to have 

 dark, or black pigment, or to be transparent, as in pelagic animals; 

 those living upon green objects being green, etc. That this coloration 

 Ì8 not due primarily to naturai selection is shown by the remarkable 

 modification in color undergone by those animals kept in confinement, 

 the change being due without doubt to the change in color of surround- 

 ings, and hence the color of light received, rather than to changes in the 

 amount or quality of nourishment. The absence of color in those ani- 

 mais which live in absolute darkness, as in deep caves, is very signi- 

 hcant. It would be of great vaine to show whether any colorless cave 

 animals regain to any extent their pigment when brought iuto the light. 

 That cave animals are colorless and blind is in direct contrast with the 

 fact that animals from the deep sea, where there is, presumably, no 

 light, are often provided with large visual organs, and are almost in- 

 variably intensely colored with red and purple pigments. If then this 

 color of the pigment depends upon the nature of the light received, and 

 there seems to be very good reason for believing it, then we must 

 suppose that certain rays of light, the red, purple and ultra-violet ones, 



