TI 1 K MUSCULAR ACTIVITY AND OXYGEN CONSUMPTION OF URECHIS CAUPO VICTOR E. HALL (Prom the Physiological Laboratory of the Hopkins Marine Station, Pacific Grove, Calif.) I. INTRODUCTION: NATURAL HISTORY Urccliis caiifo, a large marine echiuroid worm recently discovered on the California coast by Fisher and MacGinitie (1928), presents by virtue of its habits of life a unique opportunity for the quantitative study of the interrelations between muscular activity, rate of metabolism rind the mechanism of exchange with the environment. The animal digs and lives in a U-shaped burrow in the mud of shallow estuaries, leaving it only occasionally to construct a new burrow. The upper ends of the burrow open freely to the water. The requisite exchanges with the environment: respiratory, nutritive, excretory and reproductive, are accomplished by the animal forcing a stream of water through the burrow. The movement of water is produced by peristaltic waves in the musculature of the body wall, originating at or near the anterior end, and passing posteriorly. The integument in the region between two consecutive waves is pressed closely against the wall of the tube. Accordingly, water between the integument of the constricted regions and the sides of the burrow is carried posteriorly with the peristaltic wave. The worm from time to time turns around in the tube, thus reversing the direction of the stream. The mode of feeding is unusual. Near the anterior end of the worm there is a ring of specialized mucous glands. The animal presses the body wall in the region of these glands firmly against the side of the burrow; then, as the glands secrete, it hacks away, leaving a tube of mucus attached to the burrow at one end, and to its integument at the other. The peristaltic movements, usually suspended during the forma-tion of the tube, are no\ v resumed, drawing a stream of water through the mucus tube, which acts as a filter. Particles over one micron in diameter an-retained. After filtration of water has continued for some time, the worm moves forward, seizes the tube with the proboscis and s\vallo\\-s it whole. Since the food consists of particles included in the detritus of the estuary bottom, this mechanism enables the animal 400
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