242 Fortieth Annual Meeting 



the color tone assumed by the fish. A flounder placed in a 

 black-bottomed dish becomes dark, whether in a dim corner 

 of the room or in the full light of day. Conversely, a fish 

 becomes very pale upon a white surface, whether this is 

 brilliantly illuminated or heavily shaded. This fact has 

 already been pointed out by other observers, and indeed it 

 would seem to be a necessary state of affairs, in order that 

 the coloration should be adaptive or cryptic. For it is 

 obvious that the fish is shaded or illuminated equally with 

 the surface on which it lies, so that the relation between the 

 two remains unaffected by the degree of illumination. 



A rather curious corollary may be drawn from this last 

 principle. Suppose that we have two aquaria side by side, 

 one with its inner surfaces painted white, the other painted 

 a perfectly neutral gray. Suppose that the white aquarium 

 is heavily shaded, so as to admit comparatively little light, 

 while the gray aquarium is fully exposed to the light 

 (indeed, a reflector was used in my experiments). Never- 

 theless, the fishes in the white tank should assume the 

 minimum degree of pigmentation, while those in the gray 

 tank should continue to display a certain amount of their 

 dark pigment, depending upon the depth of the gray em- 

 ployed. Experiment shows that this is precisely what hap- 

 pens. The fishes in the shaded white tank become nearly 

 white, those in the gray tank become gray. It is obvious, 

 however, that the dimly-illuminated white walls of the one 

 tank are actually darker than the brightly illuminated gray 

 walls of the other tank, in the sense that the former reflect 

 an absolutely smaller amount of light than the latter. (In 

 my own experiments I have photographs showing this to be 

 true.) An extremely interesting problem is involved here, 

 which cannot, however, be discussed within the limits of 

 the present paper. 



A word in regard to the utility of this power of color 

 change in the life of the organism. It is difficult to doubt 

 either that this faculty has some use. or that it has been 

 developed in some way because of its u.se. The end attained 



