146 



THE PHYSIOLOGY OF EARTHWORMS 



necessary for this action passing along the ventral nerve cord for at 

 least thirty segments at a rate of about 25 mm/sec. Thirdly, if the 

 ventral nerve cord is removed completely from several segments 

 leaving the rest of the segments intact, the co-ordination of front 

 and rear is not affected (Friedlander, 1894; Beidermann, 1904; 

 Garrey and Moore, 1915; Moore, 1923a). It is therefore apparent 

 that the peristaltic wave can be propagated from segment to 

 segment either along the nerve cord via the intermediary neurones, 

 or by mechanical stimulation of the succeeding segments. 



Fig. 47. Effect of weight on muscular movements of Liimbricus 

 (after Moore, 1923a). 



Gentle tactile stimulation of the surface of a worm will induce 

 movement of the body, but anaesthesia with MgCl2 blocks this 

 response. If such an anaesthetized worm, or piece of worm, is 

 now suspended vertically and weight is applied to the posterior 

 end a peristaltic wave is set up (Fig. 47). Thus both touch and 

 tension induce contraction though tactile stimulation first causes 

 extension, whilst tension causes contraction. If the experiment is so 

 arranged that the ventral nerve cord alone is stretched no peri- 

 stalsis begins. This leads one to suspect the presence of intradermal 

 receptors, possibly in the deep muscle layers. Dawson (1920) has 



