48 THE PHYSIOLOGY OF EARTHWORMS 



nitrogenous compounds has not been determined in the small 

 quantities available by this micropipette method. 



The losses to evaporation and dilution by excess fluid are, how- 

 ever, minimal in the experiments of Cohen and Lewis (1949 a, b) 

 and Needham (1957) but somewhat conflicting results have 

 been reported by these workers. Normal, healthy, fed L. terrestris 

 excrete an average of 5-75 /xg NHs/g wet wt./day, which represents 

 approximately 70-80% of the total non-protein nitrogen. Urea 

 accounts for about 8% of the total (0-37 jug/g wet wt./day): 

 Cohen and Lewis (1949 a, b) record 0-16 /^g/g wet wt./day allantoin 

 and 0-113 fig/g wet wt./day uric acid, substances not found by 

 some other authors. A period of starvation is followed by an 

 inversion in excretion of the major constituents, ammonia falling to 

 1-8 /zg/g wet wt./day, whilst the urea fraction rises to 18-15 fxg/g 

 wet wt./day. At the same time the total amount of non-protein N 

 excreted rose from 7-4 fxglg wet wt./day to 21-5 fig/g wet wt./day. 



Very different absolute values were obtained, however, for the 

 same species, by Needham (1957). Estimates of the total non- 

 protein nitrogen content of urine in animals feeding on elm leaves 

 amounts to 94-8 fMg/g wet wt./day and starvation raises this level 

 to 159-2 fjLglg wet wt./day. The major components of nitrogenous 

 excretion are confirmed as ammonia (54 /xg NHs/g wet wt./day) 

 and urea (40-8 fjcg/g wet wt./day). Starvation of the animals alters 

 the relative importance of these two substances, the output of 

 urea rising by some 300% whilst ammonia decreases 30%. Thus 

 although ammonia is present in excess of urea in normal feeding 

 earthworms and the changes seen upon starvation are in the same 

 direction as those noted by Cohen and Lewis (1949b), they differ 

 considerably in the ratios of NH3 : urea, and in absolute values by a 

 factor of approximately 10 (Table 7). 



In his 1957 paper Needham reports on observations made on 

 two species of earthworms, L. terrestris and E. foetida. These two 

 species are fairly closely related but show dissimilar patterns of 

 nitrogen excretion. Table 7 compares the nitrogen output of these 

 two species and reveals that whilst the urea production of the two 

 forms is closely similar there is a considerable discrepancy between 

 the ammonia released by each species, that of E. foetida being 

 double that of the much larger L. terrestris. Needham finds no 

 evidence that the roles of urea and ammonia are interchanged in the 



