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Published online by Cambridge University Press: 17 January 2013
Some months ago, in investigating the anatomy of the eyes of fishes, I washed off the back silvery part of the choroid coat of the haddock, with a hair pencil, and about half a teaspoonful of water. The latter became of a milky colour, and on examining a drop of it, with an Ellis's aquatic microscope, I found the milkiness to be owing to innumerable slender, flat, silvery spicula, which had composed the substance of the choroid. They seemed to be in constant motion, apparently rolling upon their axes, but having no degree of progressive movement. The light reflected from their surface was very brilliant, like that from polished silver, and often disappeared, and again returned, with alternations so rapid, as to produce a twinkling, very like that of a fixed star.
page 385 note * “Of all vertebral animals,” says this illustrious physiologist, “fishes are the most remarkable for the brilliant and metallic colours which their rete mucosum exhibits. We find in them gold, silver, and copper, tin, lead, and even all the tints which these metals assume in different degrees of oxydation. But as the description of these colours is the province of Natural History, properly so called, we wish merely to point out in this place, that they are produced by the mucous substance which adheres closely to the internal surface of the scales, and with which it is frequently renewed.” Sect. XIV.
