Retinomotor and Diurnal Rhythm in Crustaceans

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Abstract
The demonstration of the existence of a diurnal rhythm in the migration of the pigment in Leanab, Portunus, Pachygrapsus and Careinus justifies the supposition that in many species of Crustaceans such a rhythm exists in the retinomotor changes of one of the pigment systems. These periodic changes in the position of the pigment, despite the exclusion of all light, correspond with sunrise and sunset. Even if the animal is kept in complete darkness during the hours of daytime, the pigment systems concerned exhibit a partial migration towards the position of light-adaptation; when the night returns the pigment system resumes its maximum state of dark-adaptation and is found in the same position as in the previous night. The measurement of the size of the pseudo-pupil is of value in proving, in vivo, the existence of a diurnal rhythm in the iris pigment. The existence of a periodic change in the luminosity of the living eye when examined with the ophthalmoscope is of no value in ascertaining the occurrence of a diurnal rhythm in the retinal pigment or in the tapetum. In C. maenas it was possible to demonstrate a periodic variation in metabolism, in terms of a diurnal rhythm in the production of carbon dioxide. This production was about 30 % smaller during the day than during the night. The diurnal retinomotor rhythm may depend on a periodic hypoxaemia of the cell systems concerned.

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