A PERSISTENT DIURNAL RHYTHM OF CHROMATOPHORIC RESPONSE IN EYESTALKLESS UCA PUGILATOR

¹ Department of Physiology and Bacteriology, Goucher College, Towson 4, Md.; Department of Biological Sciences, Northwestern University, Evanston, Ill.; and the Marine Biological Laboratory, Woods Hole, Mass.

1. The responses of the black chromatophores of Uca pugilator as observed in legs autotomized and maintained in sea water are described.

2. The pigment in legs from normal animals in the day (dispersed) phase becomes concentrated after isolation; that from normal animals in the night (concentrated) phase remains concentrated.

3. The pigment in legs isolated from eyestalkless animals disperses in the daytime and fails to disperse when the legs are removed from 8 P.M. to 2 A.M.

4. The activity on eyestalkless animals of a series of concentrations of eyestalk extract was determined in the daytime and at night. Four of the six concentrations tested were found to be more effective in the daytime than at night.

5. The results clearly demonstrate the existence of a diurnal rhythm in eyestalkless animals and that the structures of the eyestalk are not necessary for this rhythm.

6. The data provide strong evidence that a black-pigment-concentrating substance participates in the regulation of the chromatophore system of these animals.