Studies on the Diurnal Rhythm of the Eye Pigments of the Shrimps. (Preliminary Report)

Persistence of a diurnal rhythm in the migration of the retinal pigments of several crustaceans, in spite of constant conditions of illumination or of darkness is known. The distal pigment and the reflecting pigment in the eyes of three shrimps, Leander paucidens, Paratya compressa, and Spirontocaris alcimede, continue their characteristic movements under constant external conditions. These movements are able to analyse by some experimental methods. The regularly recurring 24-hour cycles in pigment migration in the eye of these shrimps might be due to regular variation in the activity of nervous inhibitory centers causing a variation in the amount of hormone released from the gland of the eye-stalk.