THE AXIAL FIELD 39 



and in Stylochiis Watanabe and Child (1933) demonstrated a 

 similar curve for CO 2 output, indophenol oxidase reduction and 

 KCN susceptibility along the length of the animal. Strelin (1938), 

 however, was unable to obtain similar results using dye techniques 

 on Limnodriliis and Tuhifex. 



It is obvious that if a gradient or polarity exists between the 

 anterior and posterior ends it may have considerable importance in 

 the process of regeneration when the normal picture is disturbed 

 and several workers have concerned themselves with this aspect of 

 the problem. 



The freshly cut end of an earthworm is generally electronegative 

 with respect to the neighbouring uninjured segments (Morgan and 

 Dimon, 1904) and this observation was extended to cover the 

 body by Watanabe (1927). In E.foetida the anterior end is electro- 

 negative with respect to the posterior end on the dorsal surface. 

 Ventrally the negativity is greatest at the anterior end, falls in the 

 mid-region (segments 65-70) and then rises again towards the rear 

 end. In fact the curve is U-shaped. 



This variation in the electrical potential was confirmed by 

 Moment (1949) also working on E.foetida, and he noted that the 

 potential decreased from +15 mV to —11-8 mV immediately after 

 the worm was divided at the 50-51 segment furrow. As regenera- 

 tion of the rear end proceeded so the potential steadily returned to 

 its original level, reaching this point after approximately 3 weeks. 

 After this time, although the animal continues to lengthen no 

 further segments are added and no change in potential is seen. 



Kurtz and Schrank (1955) repeated this work and obtained 

 essentially the same results. The anterior end is 14 mV negative 

 with regard to the hind end, and the clitellar area has greater 

 negativity than the same area in non-clitellate worms (Fig. 14). 

 Upon starvation the observed voltage decreased posteriorly and at 

 the clitellum. This was particularly marked in the first 4 days of 

 starvation, but a slow constant decrease was recorded up to 30 

 days starvation. These workers, however, did not find a reversal of 

 polarity directly after severing the body at the 50-51 segment 

 region, and the regeneration process was accompanied by fiuctuat- 

 ing voltages rather than by a steady rise. When the regenerant is 

 fully grown the anterior-posterior potential may even show a rise 

 into positive values. 



