Abstract
The diurnal rhythm of feeding was examined by the removal, covering, local cauterization and local cutting of the eyestalk for clarification on the portion of the optic ganglion related to its mechanism in the prawn P. japonicus.
From the results of the removal and covering experiments, it was confirmed that the eyestalk participated endogeneously in the maintenance of the prawn's diurnal rhythm. The local opera-tions of cauterization and cutting indicated the medulla terminalis of the optic ganglion as the essential site of the mechanism, because of the disappearance of the diurnal rhythm after each treatment.
Further, histological investigation was tried to identify the medullary cells as components of the mechanism for the prawns reared under two different conditions of continuous light. After rearing for 10 and 30 days, the cells revealed a significant change in the diametric ratio of the nucleus to its cytoplasm (nuceeo-cytoplasm ratio) between the day-time and night-time samplings, notwithstanding the rearing period and light condition.
The medulla terminalis was supposed to be the oscillator, or its component, of the biological clock in the prawn due to its stable rhythmicity with the cellular activity reflected from the nucleo-cytoplasrn ratio.
