Abstract
It has been known for a considerable time that in the fishes, amphibia and reptilia remarkable changes in color pattern or external appearance occur. It is also generally known that these effects are due to the reciprocal interplay of alterations in at least two great systems of pigment-bearing cells, the bearers of dark pigment (melanophores) and the bearers of various other pigments, many of them metallic lustered (xantholeucophores). To the latter class of pigments the trout owes its silvery appearance.
Somewhat over two years ago the author, followed shortly by B. M. Allen, showed that peculiar silvery frog larvæ were invariably produced when the epithelial portion of the hypophysis was removed in early embryonic stages. For the sake of brevity these individuals were designated “albinos” and are always in conspicuous contrast to the darker, normal specimens. As might be expected from our introductory remarks, both of the great groups of pigment-bearing cells contribute to produce this strange effect; but no mention of the iridescent cells (the xantholeucophores) was made by the writer at the time of his early communications on this subject 1 and it is noteworthy that in both of the subsequent papers by B. M. Allen 2 and in the recent communication by W. J. Atwell 3 these cells have received no attention whatever. 4
It can be demonstrated easily that the silvery, or albinous, condition, as is the case in so many instances of the color change in animals, is participated in by both groups of cells, melanophores and xantholeucophores. Furthermore, it is indeed a fact that under normal conditions no change in the condition of one of these sets of cells takes place without a reciprocal alteration in the other. This conception was forced home to the writer not merely by a reexamination of the anatomical causes for the albinos, but by extensive physiological and pharmacological experiments on normal and albinous specimens.
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