(With One Plate and Five Text-figures) LOCOMOTION AND THE ARREST OF LOCOMOTION

IN the earthworm, locomotion is effected by a slowly travelling wave of thinning and elongation, followed by a wave of thickening of the body. This is generally described as a peristaltic wave. At any one moment, a whole peristaltic wave does not involve more than a part of the body of the worm. The thinning phase of the wave is produced by a local contraction of the circular musculature of the body wall; a contraction which travels along the body from head to tail at a rate of between 3 and 10 cm. per sec. (Bovard, 1918). The thickening phase of the wave, which follows the thinning, consists of a contraction of the longitudinal musculature of the body wall, travelling at about the same rate. The whole movement has recently been analysed by Gray and Lissmann (1938). The worm is capable of crawling backwards by means of a movement of the same type, the wave travelling in the reverse direction, and usually described as anti-peristalsis. The time taken for a peristaltic wave to pass along the whole body is from about 3 to 7 sec. A worm presented with a noxious stimulus at the head, soon after a peristaltic wave has begun, would continue to crawl for some seconds subsequentl