46 THE PHYSIOLOGY OF EARTHWORMS 



One of the earliest attempts to ascertain the excretory products of 

 earthworms was made by Lesser (1908) on L. terrestris and E. 

 foetida. Using the hmited techniques available in those days he 

 found no evidence for the occurrence of uric acid, urea or allantoin, 

 but did obtain results indicating the presence of ammonia. Much 

 later Florkin and Duchateau (1943) showed that this was not 

 altogether surprising for earthworms possess no allantoinase, 

 allantoicase or uricase and cannot hydrolyse allantoin, allantoic 

 acid or uric acid respectively. These authors did find that xanthine 

 oxidase, the uric acid forming enzyme, is apparently available. 

 Urease has been reported by Przlecki (1923) to break down urea 

 and form ammonia at the very slow rate of 2-28 mg ammonia /1 00 

 g/day. This may have been erroneous, however, and perhaps due 

 to bacterial action for Abdel-Fattah (1957) found no signs of 

 urease activity in blood, coelomic fluid, body wall or gut of L. 

 terrestris or A. longa, although ammonia and urea were both to be 

 found in these tissues. 



The nitrogenous excretion of earthworms may be considered as 

 occurring in two fractions, each accounting for approximately 

 equal portions of nitrogen removed each day. The first portion 

 consists of a protein amounting to about 0-030 g/100 ml urine /day 

 (Bahl, 1947a, b), and is most probably derived from the mucus 

 secreted copiously by the body wall. This mucus acts as a lubricant 

 as the worm proceeds along its burrow, also helping to bind soil 

 particles together and preventing the burrow walls from collapsing. 

 Mucus also probably acts as a buffer system outside the body since 

 it is secreted in large amounts when the animal is immersed in a 

 noxious stimulant such as acid. This mucoid protein can account 

 for about half the total nitrogen lost each day (Needham, 1957; 

 Haggag and El-Duweini, 1959), though this may be a reflection of 

 the somewhat unnatural conditions encountered by the animals in 

 experimental vessels. 



The second fraction, representing the end products of metabo- 

 lism, is a fluid urine comprising a mixture of ammonia and urea, 

 with rather confused reports also on the presence of uric acid and 

 allantoin (Fig. 16). The proportions and presence of these nitro- 

 genous substances depends upon the species and upon the con- 

 dition of the animals when examined. 



Lesser (1908) and Delaunay (1934) both isolated earthworms 



