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Journal of Experimental Biology 49,657-667 (1968)
Published by Company of Biologists 1968

The Hydraulic System of Urechis Caupo Fisher & Macginitie

G. CHAPMAN ¹

¹ Department of Biology, Queen Elizabeth College, London, W. 8

1. The hydrostatic pressures recorded in the coelom of Urechis during peristalsis, irrigation, burrowing and hind-gut ventilation have been recorded continuously. The main muscular activities except burrowing take place at pressures of a few centimetres of water and, it is suggested, are mainly carried out by the outer circular muscle layer. The high pressures involved in burrowing demand the recruitment of the whole muscle system.

2. The hind-gut ventilation stops when internal pressure is raised, although changes in the contained volume of the body wall do not appear to provide information leading to the maintenance of a fixed volume. Instead this control is probably excercised by the hind gut.

3. An attempt is made to calculate the energy requirements of irrigation and ventilation and it is shown that these are small compared with the respiratory rate, indicating that the movement of large volumes of water for feeding purposes is not an extravagant way of obtaining food in terms of energy expenditure.