NITROGENOUS EXCRETION 53 



Ramsay (1949 a, b) might have a useful application here though the 

 quantities obtained would be extremely small. 



Although no information can be presented regarding the changes 

 of urine content, if any, during desiccation it is possible to show 

 that the tissue content of nitrogenous substances changes its 

 nature during such conditions. Analysis of tissue homogenates from 

 fresh A. caliginosa show that ammonia nitrogen amounts to 

 26-48 mg/g tissue nitrogen, urea 13-14 mg/g N and uric acid 1-33 

 mg/g N. These values, like those for urine content, do not change 

 during starvation (in the experiments of Haggag and El-Duweini, 

 1959). When the animals are allowed to dry in air, however, the 

 ammonia and uric acid content remain quite stable but urea 

 values rise considerably (Table 7). 



This rise in urea content can be correlated with a gradua] 

 decrease in the amount of water present suggesting that the earth- 

 worm is able to adapt its excretory pattern in times of internal 

 water stress by carrying the metabolic cycle further to produce 

 urea instead of ammonia. The production of the even less toxic 

 uric acid, however, is not affected, perhaps due to a limited enzy- 

 matic apparatus (xanthine oxidase) which is unable to deal with the 

 increased conversion required (Florkin and Duchateau, 1943). 



Haggag and El-Duweini (1959) made no differentiation between 

 the various organs of the body, homogenizing the animals entire 

 without previous separation of the parts. That there is a partition 

 of ammonia and urea between the gut and the body wall has been 

 shown by Heidermanns (1937) for L. terrestrts and by Bahl 

 (1947b) for Pheretima posthuma. Analysis shows that the gut wall 

 contains more urea than the body musculature, and also more 

 ammonia, though the differences here are not so pronounced 

 (Table 8). 



Creatinine was reported by Bahl (1947a) as a breakdown product 

 in both body wall musculature and intestine in P. posthuma^ and 

 Abdel-Fattah (1957) obtained a figure of 1-60 mg% for the creati- 

 nine content of urine from Ltimbriciis and Allolobophora. The 

 methods used in these estimations are not, however, specific and 

 with the discovery of lombricine in oligochaetes, and other 

 guanidine derivatives in sundry other annelids it is highly likely 

 that the so-called creatinine fraction is in fact some other guanidine 

 product. 



