120 THE PHYSIOLOGY OF EARTHWORMS 



have been described by Moment (1949) and Kurtz and Schrank 

 (1955). The latter authors find the region of greatest electrical 

 negativity to be the heart-clitellum region, which is — 16-OmV 

 relative to the posterior end, the mean voltage between anterior 

 and posterior ends being in the region of —14-0 mV, regardless of 

 the length of the worm [E. foetida) (Kurtz and Schrank, see 

 Fig. 7). 



When the animal is bisected, at any level from segments 40 to 

 80, the electrical potential decreases sharply but returns to the 

 original value within 3 weeks. During this period segments are 

 replaced by outgrowth from the anterior end, but after 3 weeks 

 regeneration growth ceases and the voltage remains steady at 

 about the initial level. Moment (1949) therefore concluded that a 

 certain voltage is inhibitory to the growth of further segments and 

 this controls the length of the regenerant, a conclusion also reached 

 by Kurtz and Schrank (1955) who noted a swing to electro- 

 positivity in the anterior-posterior gradient at the time when new 

 segment formation ceases. Starvation for 4 days of intact animals 

 brings about a decrease in the voltage of the posterior and clitellum 

 regions. The anterior segments, however, are unaffected by 4 

 days treatment, but, in common with the other regions, declines 

 slowly if starvation is prolonged up to 30 days. Starvation also 

 adversely affects the rate of regeneration in E. foetida although the 

 final number of segments produced is not altered since the final 

 potential is similar in both cases. 



Unfortunately there is no suggestion at present as to just how 

 such a voltage can affect the growth and differentiation of new 

 body tissue. Electrical stability must be governed by some process 

 as yet unknown. 



As noted previously, however, the nervous system controls the 

 course of regeneration. If the ventral nerve cord is removed then 

 regeneration does not occur (Zhinkin, 1936). With this in mind 

 Massaro and Schrank (1959) have investigated the effects of nerve 

 depressant and excitant substances upon the course of regeneration. 

 Lithium, well known for its inhibitory effects on the growth of other 

 organisms both vertebrate and invertebrate, depresses the number 

 of segments that develop after injury. This action would seem to be 

 due to replacement of sodium ions with lithium, and if NaCl is 

 provided at the same time as lithium (3:1) then regeneration 



