NITROGENOUS EXCRETION 47 



into large volumes of water for varying periods of time, and then 

 analysed the resulting fluid. As we have mentioned above Lesser 

 had difficulty in deciding what nitrogenous substances are present, 

 being certain only of ammonia. Delaunay (1934) found that 

 ammonia is the largest single excretory product detectable in the 

 urine, and this is allied to urea, and a little amino nitrogen. He 

 found no uric acid. Under the conditions of the experiments, 

 however, considerable dilution of the urine occurred and no reliable 



NH, 

 CO 



HN — 0=0 

 = C C— NH. 

 HN — C NH 



,N 



"' II 

 C C— NH 



X^ 



HN- CH-NH 



Fig. 16. Formulae of ammonia, urea, uric acid and allantoin, the 

 presence of which have been reported in the urine of earthworms. 



estimate can be made as to the volume and chemical concen- 

 tration of the urine produced. More recently results on urine 

 composition have been obtained from earthworms placed in small 

 volumes of water (Needham, 1957), in clean flasks washed out 

 periodically (Cohen and Lewis, 1949b), in moist air with urine 

 allowed to drain away down a slope (Bahl, 1947a) and by collection 

 of urine direct from the nephridiopores (Ramsay, 1949a). Unfor- 

 tunately the last-named method, by far the most accurate technique, 

 has been used so far only for estimating the osmotic pressure 

 and mineral salt content of the urine, and the concentration of 



