. Bulletin of the Bureau of Fisheries. Fisheries; Fish culture. HISTOLOGICAL BASIS OF ADAPTIVE COLORS IN PARALICHTHYS ALBIGUTTUS. ^ In a fully contracted melanophore all the pigment is concentrated in the central area. A fully expanded xanthophore (fig. 2, pi. i) may or may not show a pigment-free area at the center. The central pigmented area is usually more or less irregular in outline and from it relatively few irregular processes radiate. The pigment granules show no regular arrangement. Xanthine granules disposed along definite radial lines are rarely observed. In a fully contraced xantho
. Bulletin of the Bureau of Fisheries. Fisheries; Fish culture. HISTOLOGICAL BASIS OF ADAPTIVE COLORS IN PARALICHTHYS ALBIGUTTUS. ^ In a fully contracted melanophore all the pigment is concentrated in the central area. A fully expanded xanthophore (fig. 2, pi. i) may or may not show a pigment-free area at the center. The central pigmented area is usually more or less irregular in outline and from it relatively few irregular processes radiate. The pigment granules show no regular arrangement. Xanthine granules disposed along definite radial lines are rarely observed. In a fully contraced xanthophore the pigment is all concentrated in a more or less irregular mass in the central area. Both melanophores and xanthophores can be observed in any phase intermediate between maximal expansion and maximal con- traction. Guanophores are cells or groups of cells which contain guanin in the form of minute crystals. They occur either isolated or in groups and are frequently associated, more or less intimately, with chromatophores. Guanophores are sufficiently abundant in the superficial layers of the skin to occupy a relatively large part of the surface area. They also possess the capacity to contract and expand to a certain degree. When a fish changes from a darker to a lighter shade more or less rapidly, the guanophores occupy less of the surface area and appear somewhat more compact in the latter than in the former condition. The number of guanophores in the superficial layer of the. Fig. z.—Diagrammatic drawing illustrating the distribution of chromatophores and guano- phores in a longitudinal section of the skin of Paralichthys albiguttus. (i. epidermis; 2, 4, layers of chromatophores and guanophores superficial to scales; 3, s, 7, scales; 6, 8, chroma- tophores and guanophores in the deeper layers of the skin.) skin apparently varies somewhat with the shade assumed by the fish if that shade is maintained for a sufficient length of time. In a fish which has for some time a
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