CHAPTER IV 



THE AXIAL FIELD 



The metamerically segmented body of the earthworm, with its 

 serially repeated organs occurring along the length of the body, 

 and with a certain degree of specialization at the anterior end, has 

 been a favourite choice for investigators concerned with activity 

 gradients, or fields, in bodily functions. From analysis of the 

 reactions of the tissues to poisons, the electrical properties of the 

 body, respiratory rates, or even chemical content, it has many times 

 been postulated that an axial field of dominance is exhibited in 

 oligochaetes, the anterior end exerting a controlling effect over the 

 rest of the body. This is of particular importance when considering 

 the phenomenon of regeneration, a process believed to be governed 

 by the disturbance of a static axial gradient. Even now, however, 

 there is disagreement as to the existence of such gradients, let 

 alone the influence of such states. 



In 1916 Hyman investigated the effects of cyanide upon several 

 species of oligochaetes including Dero, Lumbrtciihis, Tubifex and 

 Limnodrilus. She found that the susceptibility of the tissues of 

 these w^orms was not constant and that death occurred most 

 quickly at the anterior end, the more posterior segments resisting 

 cyanide poisoning relatively longer (Fig. 13). At the very rear end 

 the segments were rather more sensitive to cyanide than in the 

 mid-region of the body and consequently a U-shaped curve was 

 obtained, with the most sensitive regions at front and rear, and the 

 most resistant region in the middle of the length. On this basis 

 Hyman suggested that the more rapidly metabolizing portions of 

 the body were the most sensitive. 



Shearer (1924) therefore undertook to study the respiration 

 rates of pieces of earthworm taken from various regions along the 

 length of the body. Using a Haldane gas analysis apparatus he 

 examined both live segments and acetone powder extracts from the 



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