62 THE PHYSIOLOGY OF EARTHWORMS 



rises when this amine is injected into the alimentary canal, and 

 rises further still when another nitrogenous compound is injected 

 simultaneously. Arginine and alanine injected into the alimentary 

 canal can both increase the excretion of urea (Abdel-Fattah, 1955). 

 The only enzyme yet demonstrated in this cycle is arginase 

 (Cohen and Lewis, 1950), but it is possible that citrulline is 

 degraded very rapidly and thus is always at a minimal level in the 

 cells, accounting for its non-demonstration. On the other hand 

 some completely unexpected detoxication mechanism may be in 

 force, and Needham (1960) suggests that the cycle may be halted 

 at the ornithine stage, thus accounting for the lack of citrulline. 

 The actual role of the chloragogen cell in the nitrogenous metabo- 

 lism of the earthworm has recently been questioned in work done 

 by Needham (1962). The part played by the enzyme arginase in the 

 Krebs— Henseleit system has been mentioned above, and it has 

 been shown to occur in extracts of chloragogen cells. The results of 

 Needham (1962) indicate that the occurrence of arginase activity 

 along the body of the earthworm is the mirror image of the 

 presence of chloragogen, and it seems possible that this enzyme is 

 associated with the gut wall. 



From the observation discussed above it can be reasoned that the 

 chloragogen cell is indeed liver-like (Roots, 1960). It is evidently 

 involved in storage and metabolism as shown by its vast glycogen 

 reserve and fat store, the concentration of acid ATP'ase indicates 

 that it is a highly active tissue, and the concentration and variation 

 of ammonia and urea content shows that it is taking part in 

 detoxication mechanisms. It would be interesting to know the 

 effects of removal of the chloragogen tissue on an oligochaete. 



Removal of waste Products 



If then, as it seems likely from the analyses above, the ammonia, 

 urea and other nitrogenous compounds of the urine are formed in 

 the chloragogen cells, how are these substances transported to the 

 organs of excretion, the nephridia that open through the body wall 

 or into the gut in some species? 



Estimations made of the nitrogenous substances of the coelomic 

 fluid and of the blood show that in both these systems there is less 

 ammonia and urea than is available in the excreted urine, but that 

 creatinine (? other guanidine) is at a lower level in the urine. 



