40 



THE PHYSIOLOGY OF EARTHWORMS 



Both Moment (1949) and Kurtz and Schrank (1955) consider 

 that the resuhs outHned above support a thesis that the formation of 

 new segments in response to a loss of part of the body is correlated 

 with the electrical potential of the intact body. The average 

 number of segments regenerated by E. foetida lies between thirty- 

 three (Kurtz and Schrank, 1955) and forty (Moment, 1949), and 



Fig. 14. The longitudinal distribution of electrical potentials of 

 earthworms measured on the dorsal side with the posterior end 

 earthed. Each point represents an average of 200 measurements and 

 standard deviations are shown by the vertical lines. Small circles 

 on the vertical lines show the reliability of the means at 5% 

 level of confidence. The regions are located thus: A, segments 

 2-4; B, segments 8-12; C, 20-23: D, 26-32; E, 35-38; F, 1cm. 

 posterior to E; G midway between F and H; H, 1 cm. anterior to 

 L; hindmost 4-5 mm (from Kurtz and Schrank, 1955. Copyright 

 1955, University of Chicago). 



the final voltage difference between head and tail reaches 20 mV 

 (Kurtz and Schrank, 1955). These authors suggest that when fully 

 grown a critical voltage has developed between the extremities and 

 this inhibits further prolongation by the addition of fresh segments. 

 It would be interesting to know what the voltages are in young 

 growing worms and whether a similar voltage difi^erence exists 



