On the Nervous Control of the Velar Cilia of the Nudibranch Veliger

Abstract

(1) The beat of the velar cilia of the Nudibranch veliger is intermittent and appears to be under the control of the organism. (2) Fibres lying between the cells which bear the velar cilia are described. They end near the outer surface of these cells in fibrils which resemble those of the muscle-plate in structure. They stain with specific nerve-stains and were shown to be in all probability continuous with nerves lying deeper in the tissues. It is concluded that these are nerve-fibrils. (3) Within the ciliated cell at the level of the terminal fibrils of these fibres there is a layer of granules which stain with methylene blue. (4) The cilia of cells which have been separated from the tissues beat actively but the beat is continuous and not intermittent. (5) In the presence of various narcotics the intermissions are inhibited more quickly than the beat of the cilia is affected and at a lower concentration of the drug. (6) Some drugs which are not known to act as narcotics were used and with certain exceptions, which are discussed, did not have this effect. (7) In an acid medium the beat is slower but the intermissions continue so long as the cilia beat. (8) In an alkaline medium the intermissions are inhibited before the beat is affected. This is discussed and it is suggested that it is in accordance with recent work on the effect of changes in the reaction of the medium on nerve-tissue. (9) It is concluded that the nerve-endings found among these cells are regulatory and are concerned in the causation of the intermissions. The beat of the cilia is therefore under the control of the nervous system of the animal.