THE AXIAL FIELD 



43 



in this region, whilst the mid-portions of the body, containing 

 the unspecialized intestine and nephridia might be expected to 

 have a lower metabolic rate, but apart from Needham's idea of a 

 posterior penultimate control centre no one has yet suggested the 



40 



30 



20 



Ant. 



Muscle 

 glycogen 



I Visceral 

 u glycogen 



Lipoid (whole worm) 



10 20 30 35 



45 



90 



Segment level 



Fig. 15. Muscle glycogen, visceral glycogen and "whole worm" 

 lipoid related to segment level. Clitellar zone extends from seg- 

 ments 29 to 36. Each zone analysed consists of approximately 10 

 body segments. The posterior zone contains the last ten segments 

 (usually 100-110). Histograms represent mean of five separate 

 analyses; for each analysis large non-clitellate specimens of E. 

 foetida were used. Glycogen estimations thirty worms per lot. 

 Lipoid estimations twenty worms per lot. Results expressed as 

 mg/g wet weight of worm tissue (from O'Brien, 1957a). 



cause for heightened activity at the rear extremity. It is generally 

 true that in pigmented species the hind end contains more coloura- 

 tion than the mid-regions and this may be correlated with light 

 sensitivity, particularly useful in species casting on the surface, 

 such as A, longa. 



Summary 



Axial gradients have been reported in many of the various 



