. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. Vertical section through one arm of a starfish; b, ampulla; d, water canal opening at maJre- poric plate {st); i, radial water tube; m, mouth; ft, tube feet; py, digestive gland; stc, stomach. Davison, Zoology. On the dorsal (aboral) side of the animal you will find a raised body about the diameter of a pencil. This body, which under the microscope has the structure of a very fine sieve, is called the madreporic plate. Through this plate water passes into a system of water tubes and reservo
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. Vertical section through one arm of a starfish; b, ampulla; d, water canal opening at maJre- poric plate {st); i, radial water tube; m, mouth; ft, tube feet; py, digestive gland; stc, stomach. Davison, Zoology. On the dorsal (aboral) side of the animal you will find a raised body about the diameter of a pencil. This body, which under the microscope has the structure of a very fine sieve, is called the madreporic plate. Through this plate water passes into a system of water tubes and reservoirs. These tubes extend ultimately into the rays, there ending in the individual tube feet. Method of Locomotion. — If we could examine the connection of a tube foot with the system of water canals, we should find that water pass- ing from the canals in the rays flows into a tiny receptacle connected with the tube foot. If the tube foot is to be extended, the muscles in the wall of the ampulla (the receptacle next the tube foot) contract. This forces the water out, closing a tiny valve on the side of the radial canal and sending the water into the tube foot, thus causing it to lengthen. The end of the tube foot is composed of a little disk of muscle, thicker at the outer side than on the inner. When this disk is placed against an object, and when water is withdrawn from the tube foot into the ampulla, the disk becomes fastened again by suction. If now the muscles in the wall of the tube foot contract, and this process takes place simultaneously and in hundreds of the feet, it can be seen that the body of the starfish is drawn forward a short distance. To release the tube foot water is pumped in from the ampulla by the process mentioned above. The same act repeated again and again results in locomotion at the rate of about six inches per minute in an adult starfish. The Nervous System and its Work. — The movements of the tube feet, although not in unison, are coordinated to
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