THE AXIAL FIELD 



41 



from hatching onwards. It would also be interesting to know why 

 growth does not stop at the cHtellar region where the voltage is at 

 its lowest and the overall potential difference at its greatest. The 

 results of Moment, and Kurtz and Schrank show discrepancies for 

 the same species, and no explanation is forthcoming as to how a 

 critical inhibitory voltage may affect metabolism in the cells, nor 

 indeed whether the voltage changes are the prime mover or the 

 end result of regeneration. One hopes that some of these points 

 may be settled in the future, especially in view of the work of 

 Hubl on neurosecretory phenomena in regeneration. 



The question of metabolic gradient has been re-investigated 

 most recently by O'Brien (1947, 1957a). He examined a number of 

 systems in A. longa using modern techniques. 



Table 5 



Respiratory Rates of Various Segments of the Body of 

 A. longa (/xl./lOO mg wet wt.) (From O'Brien, 1957a) 



The last ten segments of the body respire at a rate faster than 

 that of preceding segments. As O'Brien used the Warburg 

 technique and his slice thickness was only 0-6 mm the objection of 

 Shearer (1930) and Maloeuf (1936) regarding possible muscular 

 activity is unlikely to be critical, but there are no pronounced 

 differences in his figures except that the rear end respires faster 

 than the other regions (Table 5). Removal of the hind end was 

 followed by changes in respiratory rate. The oxygen uptake of the 

 stump drops, but as the regenerant grows the respiratory rate of 

 the hind end (new tissue) rises (Table 6). Segments in front of the 

 stump remain at a normal rate of respiration. The higher values 

 obtained for the rear end are interesting in view of Needham's 

 suggestion (1957) that there may be a posterior metabolic and 

 hormonal integrating centre. 



