EXCRETION AND WATER BALANCE 



49 



Fig. 24. Diagram of nephridial capsule of Theromyzon. 

 Cy coelomic cavity of ampulla; cep, coelomic epithelium; cp^ 

 cavity of capsule; ct connective tissue; ep, lining epithelium 

 of wall of capsule ; nb, nucleus of basal cell ; nc, nephridial canal 

 cell; nm, nucleus of marginal cell. From Goodrich, 1945. 



From the work of Bradbury (1959) it seems possible that in Hirudo 

 particulate matter from the coelomic fluid is retained indefinitely 

 in the botryoidal tissue and not taken to the nephridia, as it is in 

 more primitive forms. In the Hirudidae, according to Bhatia 

 (1938) the cilia of the multiple funnels beat outwards and serve to 

 waft newly formed corpuscles into the coelomic circulation. This 

 being so, it follows that the urine passed out of the nephridia is 

 obtained entirely by filtration through the walls of the tubules and 

 that the material picked up by the coelomic corpuscles must either 

 be broken down to a soluble state or be carried to parts of the body 

 other than the nephridia. 



The chemical composition of the urine of Hirudo has been 

 determined on a number of occasions (Heidermanns, 1937). Under 

 normal conditions about 72% of the nitrogen excreted is in the 

 form of ammonia while aminoacids, purines, urea and creatinine 



