THE CONTROL OF RETINAL PIGMENT MIGRATION IN LEANDER SERRATUS

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Abstract
1. The distal and the proximal retinal pigments of Leander serratus can alter their positions in response to light and darkness. 2. The reflecting pigment shows a great movement at night which persists as a diurnal rhythm in continued darkness, but during the day it is unaffected by change of illumination. 3. The extent of distal pigment migration depends on the shade of the background on which the animal is placed, if the intensity of incident illumination is constant. 4. In constant darkness the proximal pigment continues to migrate diurnally for some days, at least. At midnight it shows a greater degree of dark-adaption than it does during the day; the distal pigment cells do not exhibit any detectable persisting diurnal rhythm in continued darkness. 5. After removal of the sinus-gland the distal pigment, in most of the operated animals, attained the position of maximal dark-adaption and was unaffected by change of illumination; it therefore appears not to respond directly to illumination. On the other hand, the proximal pigment in animals without sinus glands exhibited the same responses to change of illumination as those observed in normal animals. 6. In a series of experiments one eye of an animal was covered and the other eye was illuminated. In all the experimental animals so treated the proximal pigment of the exposed eye became light-adapted, but that of the covered eye attained the position of dark-adaptation observed in animals kept in darkness during the day. 7. A slight difference between the position of the distal pigment in the exposed eye and the covered eye of an individual could sometimes be observed; the difference was most striking in those animals which were on a black background, and in those animals which were placed in a light-proof box (in darkness) with one eye protruding through the box to be illuminated. 8. The distal retinal pigment of Leander serratus does not respond directly to illumination when the sinus gland is absent, yet in normal animals direct illumination enhances the light adaptation of the distal pigment; possibly illumination sensitizes the distal pigment cells to the hormone by which they are activated. The migration of the proximal pigment under illumination appears to be independent of the sinus gland. The influence of direct illumination on the proximal pigments appears to be great.
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