STUDIES IN THE PIGMENTARY SYSTEM OF CRUSTACEA

II. DIURNAL MOVEMENTS OF THE RETINAL PIGMENTS OF BERMUDAN DECAPODS

¹ From the Bermuda Biological Station for Research, Inc., and the Biological Laboratories, Harvard University

1. Persistence of a diurnal rhythm in the migration of the retinal pigments of several Bermudan crustaceans, in spite of constant conditions of illumination or of darkness, is reported. Two macrurans, a new species of Eusicyonia and Trachypeneopsis mobilispinis, show the distal retinal pigment in the position characteristic for the dark-adapted eye when the retinas of illuminated specimens are fixed at night.

2. Four species of brachyurans, Portunus anceps, P. depressifrons, Parthenope serrata, and Calappa flammea, show the distal and the proximal pigments in the typical light-adapted position when the specimens are kept in the dark-room and are fixed during the day.

3. The retinas of some of the macrurans showed deficiencies or absence of the reflecting pigment. This is thought to be due to differences in metabolism rather than to fixation artifacts.

4. Hormones are considered as the possible mediating agency involved in the phenomenon of persisting diurnal retinal rhythms.