NITROGENOUS EXCRETION 63 



Protein is at a very much reduced level in the urine, and a great 

 deal of v^hat is present probably arises as the mucus secretion of the 

 body v^all (Table 9). It is, therefore, obvious that a filtering 

 process is going on somewhere in the body. 



Waste materials can arrive at the nephridia by one or more of 

 three methods : via the blood system to the walls of the excretory 

 organs, by the chloragogen cells that disintegrate or via the coelomic 

 fluid. The disengagement of chloragogen cells from the surface of 

 the alimentary canal has been described by Cuenot (1898) and 

 by Liebmann (1946); the cells fall into the coelom and there 

 disintegrate to release the contents into the fluid of the coelom, but 

 Abdel-Fattah (1955) does not think that such actions occur. Earth- 

 worms allowed to feed upon a mixture containing iron saccharate 

 absorb it into the alimentary canal walls, and it is also traceable in 

 the chloragogen cells, but in no case free or in coelomic corpuscles. 

 It is thus unproven that the chloragogen does indeed break down 

 in the coelom, and in so doing releases excretory products for 

 removal via the nephridia. 



On the other hand, urea and ammonia are formed in the chlora- 

 gogen, and find their way somehow into the coelom. This may 

 occur by diffusion from the chloragogen, or by filtration from the 

 blood system. The latter idea would require some special mechanism 

 for allowing the passage of only nitrogenous materials. Only the 

 blood contains large amounts of glucose, amino-acids and fats, 

 but both blood and coelomic fluid contain ammonia and urea in 

 similar quantities (Bahl, 1947). Abdel-Fattah (1955) believes that 

 the blood system is the transport system for the waste products of 

 tissue metabolism and filtration occurs at the nephridia. This 

 would seem to be the obvious method in oligochaetes with internally 

 closed nephridia e.g. Megascolex caeruleus or Hoplochaetellay but 

 in species like Lumbricus the possibility of the coelomic contents 

 being removed down the lumen of the nephridia by the beating of 

 the nephrostome cannot be completely discounted, particularly 

 since the chemicals are in solution in the coelom and are not con- 

 tained within the cellular entities. 



The Function of the Nephridia in Excretion 



The nephridia are arranged segmentally within the oligochaete 

 body and good descriptions of the various modifications and 



