Spontaneous Squirting of an Ascidian,Phalliusia MammillataCuvier

Abstract

The previous work on spontaneous activity in ascidians is briefly reviewed: there is clear evidence for the existence of spontaneous contractions of the siphons of certain monascidians but no function has been ascribed to this activity.Phallnsia mammillataexhibits spontaneous contractions of its siphons at intervals of 6-9 min. over long periods in Plymouth tank sea water. The siphon contractions are synchronous. The frequency of the contractions may shift fairly quickly under constant conditions to a higher or lower rate which is usually twice or one half the normal rate.A method of recording the volume of water propelled by spontaneous activity is described. The method also records the ciliary through-current at the same time as the squirts.The frequency of the squirting is increased during a period of partial or complete starvation. It is reduced again by adding food cultures to the water.The physiological mechanisms involved in the spontaneous activity are investigated and comparisons are made with the spontaneous activity exhibited byMetridium senileandArenicola marina. It is finally suggested that the spontaneous squirting of certain ascidians is an integral part of their feeding mechanism.