56 



THE PHYSIOLOGY OF EARTHWORMS 



migration may transport the nutrients through the body or which 

 may release these substances into the blood stream or coelomic 

 fluid, controlling the amount in circulation by homeostatic means. 

 The second theory holds that these cells are excretory in function 

 gathering waste products, which are presumably circulating 

 freely in the blood, or coelomic fluid, concentrating them, trans- 

 forming them when necessary into urea, or ammonia and then the 

 cells detach from the gut wall to autolyse in the coelom from whence 

 the fluid is voided via the nephridia. As high levels of urea and 

 ammonia have been reported for both blood and coelomic fluid it is 



Uptake from Intestinal 

 wall / 



Alkaline phosphatase 



Intestinal wall 



Ammonia 

 c l/^M/IOmg 



Urea 



0-2/^M/IOmg 

 7 methyl xanttiine 



Uric acid 



CHLORAGOGEN 

 CELL 



Water dependence 



IVIuscovite 



Fig. 18. Role of chloragogen cell in metabolic relations of the 

 earthworm. 



possible that both fluid systems serve to bring waste products to 

 the nephridia, one from the tissues by means of blood vessels, and 

 the other from the internal coelom. In earthworms with nephridia 

 that are closed internally, of course, it is not possible for the 

 coelomic fluid to play a part in excretion by simple filtration, only 

 by bathing the nephridia so that diffusion can occur across the 

 nephridial wall into the lumen. 



What actually happens in the chloragocytes is probably a 

 mixture of both the above points of view as indicated by the work 

 of van Gansen (1956, 1957b, 1958) and Roots (1957, 1960) (Fig. 18) 

 with which we shall be mainly concerned here, although Liebmann 



