160 



THE PHYSIOLOGY OF EARTHWORMS 



The difference in conduction rate between the two types of giant 

 fibre is thought to be a function of the diameter of the axon, the 



fqm fgi 



Fig. 50. Sensory input of median giant fibre (black) and lateral giant 

 fibres, (a) in anterior sixty segments sensory neurons feed into 

 median giant, (b) in segments to the rear of No. 60 the sensory 

 nervous feed the lateral giants. fgl = lateral giant fibre; fgm= median 

 giant fibre; ng=giant neurone; np = neuropile. The muscular 

 envelope of the nerve cord is in black (from Grasse, 1959, after 

 Adey, 1951). 



median giant being larger and conducting faster. Adey (1951) 

 examined a number of fibres in Megascolex for speed of conduction 

 in relation to diameter and found a linear relationship, which did 



