l6 BULLETIN OF THE BUREAU OP FISHERIES. 



is relatively short. Microscopic examination of the color-producing elements in the skin of 

 specimens which had been on the black background two or three days showed conditions 

 essentially identical with the conditions of the color-producing elements in the skin of speci- 

 mens which had been kept on a black background continuously for a period of 2 1 days. 

 The accompanying figure (text fig. 6) is an attempt to illustrate the vertical dis- 

 tribution of chroma tophores and guanophores in the layer just beneath the epidermis 

 and in the layer just beneath this one overlying the proximal area of a scale in the skin 

 of a specimen which was thoroughly adapted to a black background. The solid areas 

 represent melanin pigment, the stippled areas include both xanthophores and guano- 

 phores. Figure 3, plate i, represents a camera lucida drawing of chromatophores and 

 guanophores in the layer just beneath the epidermis in the skin of a specimen 23 cm. in 

 length which had been kept on a black background for a period of 2 1 days. 



FISH ON WHITE BACKGROUND. 



The specimens used in this study were kept for intervals varying from 5 to 25 days 

 in a wooden aquarium the bottom and sides of which were painted white. Because of 



sediment in the water the bottom and sides 

 _ -^^__ ^ ^ of the aquarium assumed a brownish- 



^S^itt^^ji/'i^^^i- .{'■^^^•^"^■-jf^^m'^.. -^^m^"^ yellow tinge. Consequently, the back- 

 ground to which these specimens became 

 adapted was not pure white. When fully 

 _ adapted to this background, the color of 



"^tatvfipa -4i»«^i>.'^-'-'^^ •^HSP***^'* ^^ these specimens was grayish- white with a 



Fig. 6.-Camera lucida drawing iUustrating the vertical distri- brOWnish-yelloW tone, mottled with areOS 



bution of chromatophores and guanophores just beneath the q£ o SOmcwhat darker shadc 

 epidermis and superficial to the proximal area of a scale in the ^_ . , , 



skin of a specimen of Paralichthys albiimttus adapted to a black The mclaUOphoreS in the layer JUSt bc- 



background. SoUd color represents melanin pigment, stippling Qgath the epidcrmis in the skin of thcSC 

 includes both xanthophores and guanophores. 



speamens were all contracted to a greater 

 or lesser degree. In the lighter areas the majority of them were maximally contracted. 

 In this condition the pigment was concentrated in the central area into a rounded 

 mass, which usually lay somewhat deeper than the melanophores in their expanded 

 condition. In areas of a somewhat darker shade the melanophores were contracted to 

 a lesser degree. In these melanophores the major part of the pigment was concentrated 

 in the central area, while masses of pigment granules extended for a short distance into 

 the proximal portions of many of the radial processes or farther peripherally in a few 

 radial processes. Melanophores occurred not infrequently, even in the lighter areas, 

 in which the pigment was not appreciably concentrated. In these instances the cen- 

 tral area of the melanophore lay at a deeper level than the peripheral portions and 

 was deeply covered by guanophores. In the darkest areas many of the melanophores 

 remained expanded to a moderate degree. In all these conditions the melanophores 

 were obscured to a greater or lesser extent by associated guanophores. 



The xanthopores in the layer just beneath the epidermis were contracted to a some- 

 what lesser degree than the corresponding xanthophores in the skin of specimens adapted 

 to a black background, but were obscured to a greater extent by overlying guanophores. 

 The majority of these xanthophores showed a heavily pigmented central area from which 

 masses of pigment granules extended peripherally into the proximal portions of a few of 



