STUDIES ON THE DAILY RHYTHMIC ACTIVITY OF THE SEA-PEN, CAVERNULARIA OBESA VALENCIENNES. -XVIII. ONTOGENIC DEVELOPMENT OF THE DAILY RHYTHMIC ACTIVITY-

Abstract

1. The sea-pen, Cavernularia obesa VALENCIENNES, spawns in October and the eggs are fertilized in water and start to develop instantly. 2. In earlier stages of development they do not exhibit daily rhythmic activity. It appears on the 6th or 7th day after fertilization, when the tentacles just begin to differentiate. The daily rhythmic activity in the polyp stage is most remarkably shown by day-contraction and night-expansion of the tentacles. 3. The endogenous nature of the daily rhythmic activity was studied by putting the young polyps in constant darkness on the 6th, 9th, 15th and 20th day respect tively after fertilization. (i) The animals whose tentacles were differentiated in dark did not show any daily rhythmic activity. (ii) The animals, whose tentacles were differentiated in the normal day-night condition and placed in constant darkness on the 9th day after fertilization (after living under normal day-night condition for 2 or 3 days, with developed tentacles), persisted about one daily rhythmic activity cycle only. (iii) When the animals were placed in constant darkness on the 15th day after fertilization (after living under normal day-night condition for about a week, with developed tentacles), a stronger persistence of the daily rhythmic activity was observed (persistence was observed for 2 or 3 days in some case). (iv) It was impossible to get further concrete results because of difficulty of rearing the young animals in healthy condition for more than 20 days after fertilization. 4. It can be concluded that, (i) for the emergence of the daily rhythmic activity of the sea-pen it is necessary to be triggered by the environmental rhythms after the accomplishment of differentiation of organs related to the daily rhythmic activity, and (ii) the endogenous nature is more and more firmly settled in accord with the progress of development.