46 



LEECHES 



through the epidermis to the outside (Stephenson, 1930). Cordier 

 (1934) estabUshed that the walls of the narrow, ciliated tubes of 

 the nephridia perform athrocytosis, i.e. the absorption of certain 

 colloidal and other finely dispersed particles. Bahl (1947) showed 

 how fluid passing along the nephridial tubes of Pheretima has its 

 chemical composition changed (Table 1). Glucose and amino- 

 acids are completely reabsorbed and PO4, CI, Na, K and creatinine 



Table 1. Relative Concentrations of Various Substances 



IN Blood, Coelomic Fluid and Urine of Earthworms, 



AND Analysis of Urine 



* May have been derived from mucus contaminating urine. 



From Bahl, 1947. 



are absorbed to a considerable extent, along with water, leaving as 

 the chief organic elements of the urine urea, ammonia and 

 creatinine in the ratio 6-5 : 5-3 : 1. Ramsay (1949a and b) showed 

 that earthworm urine is strongly hypotonic to the body fluids 

 under normal conditions and that salt resorption takes place in the 

 distal rather than the proximal part of the nephridium. 



Returning to leeches, we find that there is no single tissue 

 corresponding to the chloragogenous tissue of earthworms. 

 Cuenot (1931) found that when ammonium carminate is injected 

 into the coelomic fluid of rhynchobdellid leeches it is taken up by 

 certain cells lining the coelomic channels and when injected into 

 Hirudo it is taken up by the botryoidal tissue. In each case these 



