Page:The Zoologist, 4th series, vol 2 (1898).djvu/427

Rh tage for protective purposes or as warning colours, for the single and sufficient reason that they are invisible." Some shore species of crustaceans are found to turn red when kept in the dark; hence Mr. Faxon is inclined to believe that in the deep-sea species the prevalence of red is "due to a modification of the pigments, induced by the darkness in which the creatures dwell, either through chemical action, or more probably through a physiological process originating in the eye, and affecting the pigment-cells by a reflex action. In either case the prime cause is a purely physical one—the more or less complete absence of light in the depths of the sea." ... To those who may enquire why deep-sea crustaceans should be red-tinted in general rather than of any other colour, Mr. Faxon quotes Pouchet's explanation, that "the pigments of the xanthic series (red, orange, and yellow) in Crustacea are contained in contractile anatomical elements—the chromatoblasts—while the blue pigment is never found in the substance of the chromatoblasts, but is held in free solution." "Under the influence of the abyssal darkness there is supposed to be so great an expansion of the red chromatoblasts that any effect from the cyanic tints is completely overpowered." Another explanation has been advanced to account for a similar colouration of the deep-sea flora. The blue colouration of the water is due to the decomposition or absorption of the red, orange, and yellow rays of light in their passage through the water, and owes its hue to those rays of high refrangibility,