The Tube Feet of Starfishes as Autonomous Organs

Abstract

From both the physiological and histological aspects of the tube feet of Asterias vulgaris, it is clear that they are autonomous organs. They are capable of varied and long response to stimuli when excised, although the response of a foot without an ampulla is less than when the feet are nomally attached. However, this is probably due to destruction or injury of the water vascular connections. Isolated feet with ampullae still attached lose none of the efficiency that normally attached feet show. The use of anesthetics that influence the animal as a whole, but leave the feet free, also strengthens the idea of an independent nervous structure in the feet. Isolated feet, cut alternately on one side and on the other so as to destroy any continuity of direct nerves, if stimulated, contract, showing that it is still possible for transmission to take place, and that this must be through some tissue whose continuity is not affected by the cuts, probably a nerve-net. Histological examination confirms this, as sense cells are found at the outer part of the epidermis, and these are connected by processes with other cells, seemingly of nervous nature, lying deeper in the epidermal layer. These latter form a loose net. The appearance-of the whole agrees with the descriptions of the nerve-net found in other animals.