STUDIES IN THE PIGMENTARY SYSTEM OF CRUSTACEA. IV. THE UNITARY VERSUS THE MULTIPLE HORMONE HYPOTHESIS OF CONTROL L. H. KLEINHOLZ 1 (From the Marine Biological Laboratory of the United Kingdom, Plymouth, England, the Stasionc Zoologica, Naples, Italy, and the Biological Laboratories, Harvard University, Cambridge, Mass.) Since the first demonstration by Perkins (1928) that the physi-ological activity of crustacean chromatophores is regulated by a hor-mone originating from the eye-stalks, numerous studies have confirmed and extended his results (for a review of the literature see Hanstrom, 1937). It was later shown (Kleinholz, 1934, 1936) that the retinal pigments of crustaceans were also under endocrine control, being af-fected by the same eye-stalk extracts which contracted 2 the chromato-phores of the integument. On the basis of independent chromatophoral response to various colored backgrounds, Brown (1935a) concluded that a number of dif-ferent hormones were concerned in the regulation of color change. Abramowitz (1937&), on the other hand, has questioned the necessity of more than one hormone in explaining the pigmentary activity of crustaceans. When the evidence available from studies of the retinal and integumentary pigments is considered, it appears that at least two different hormones might be involved. For example, while the chro-matophores of Palaemonetes vulgaris are maximally concentrated 2 and the distal retinal pigment is in the position of complete light-adaptation in animals kept on an illuminated white background, on an illuminated black background the red chromatophores are maximally dispersed but the distal retinal pigment is still in the light-adapted position. If both types of pigment cells were controlled by the same hormone, then ab-sence of the chromatophorotropic hormone from the circulation (evi-denced by the dispersed integumentary chromatophores in animals main-tained on an illuminated black background) should also result in a po-sition of the distal retinal pigment characteristic for complete dark-adaptation. 3 It is obvious, on the other hand, that the different be-1 Sheldon Travelling Fellow of Harvard University. 2 The terms " contracted " and " expanded " in reference to the condition of the pigment within chromatophores are used synonymously with the concentrated and dispersed state. 3 Kleinholz and Knowles (1938) have shown that the position of the distal intensity of incident light retinal pigment is directly proportional to the ratio, intensity of reflected light 510
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