LOCOMOTION IN BATRACHOSEPS. 28 1 



muscles in earthworms was not disturbed by removal of a small 

 piece of the nerve-cord, that the circular muscles failed to con- 

 tract only in the region where the cord was removed and that 

 elsewhere they continued to contract rythmically. If the pos- 

 terior part of such a worm lay on a smooth surface it would 

 allow itself to be dragged along by the part anterior to the section. 

 If, however, the posterior part be dragged over a rough surface, 

 moistened blotting paper for instance, its segments would begin 

 active, rythmical contractions and cooperate with the anterior 

 part in progressive locomotion. 



That one part of the body in these worms ' was not dependent 

 on the nerve-cord of the other part was still better shown in a 

 worm which was cut cross-wise into two halves. The halves 

 were fastened together again by a string. The anterior half, pull- 

 ing on the posterior half, especially when the latter lay on a 

 rough surface, would produce coordinated movements in the 

 posterior half. 



In another experiment only the posterior half was used. It 

 was placed on papers of two grades of roughness, the anterior 

 part on the rougher, the posterior part on the smoother paper. 

 A pull on the rougher paper started up locomotor contractions 

 in the foremost segments ; the other segments remained inactive 

 while being dragged over the smooth paper, notwithstanding the 

 fact that the cord was intact in the entire piece of the animal 

 which was under observation. 



These phenomena in worms with severed nerve-cords were ex- 

 plained as follows : One segment, shortening, produces a pull on 

 the next segment in the body and thereby stretches the skin of 

 that segment. This stretching process sets up sensory impulses 

 which, passing into their segmental ganglion, are reflected 

 back as motor impulses to muscles of the same segment. The 

 muscle contraction so produced in turn exerts a pull on the skin 

 of the next segment and thereby gives rise to another cycle of 

 sensory-motor impulses, which, as mere nerve-impulses, do not 

 necessarily pass beyond the boundaries of the segment where 

 they originated. And so on, from segment to segment, a motor 

 impulse started at a may be transmitted to segments /;, c, d, etc., 

 without any impulses whatsoever passing over the fibers in the 



