THE AXIAL FIELD 



37 



same areas, and from his results concluded that the anterior end 

 respired faster than the posterior end. He postulated further that 

 the anterior end possesses greater organization and a definite 

 substance is produced here that diffuses back through the body- 

 to affect the respiration of the more rearward segments, the further 

 from the head the lower the respiration rate since less material 



e 20 



No. of segments 



Fig. 13. Graph of the axial gradient of Dero limosa showing 



secondary posterior rise. Based on time taken for disintegration 



to occur when treated with cyanide (from Hyman, 1916). 



would be reaching these segments. He did not observe a further 

 rise in respiration at the extreme rear end. 



Further evidence for the dominance of head over tail was 

 adduced by Perkins (1929). He repeated the work of Shearer on 

 respiratory rates and obtained the highest values from pieces of 

 the anterior end. The rate decreased steadily the further the seg- 

 ments were from the head to about 60% of the length of the body 

 and then rose again slightly towards the rear extremity, thus 

 mimicking the curve of Hyman for poison susceptibility. Other 



