48 LEECHES 



They gave it the name hirudonine and suggested that it probably 

 serves as a phosphate acceptor rather than an excretory material. 



In leeches the act of phagocytosis by coelomic corpuscles has 

 frequently been observed but the route subsequently taken by the 

 corpuscles is less clear. Van Emden (1929) claimed that in 

 Erpohdella they pass into the lumen of the intestine. Others have 

 thought that they passed out of the epidermis or were laid down 

 as pigment, as in earthworms. A fourth possibility is that the 

 amoebocytes are swept up by the nephridial funnels and passed 

 into the nephridial capsule, there to break down their waste matter 

 and pass it into the nephridial tubules. When bacteria or carmine 

 particles are injected into the coelom of glossiphoniid leeches they 

 may subsequently be found concentrated in the nephridial 

 capsules, but in most leeches there is no opening from the capsule 

 to the rest of the nephridium, so it is difficult to see how the waste 

 products are eliminated. 



In an attempt to understand the role of the nephridial capsule 

 we must pause to consider the structure and evolution of nephridia. 

 In both earthworms and leeches they are metanephridia (Goodrich, 

 1945) consisting basically of an inner ciliated funnel leading to a 

 coiled length of tube which opens to the exterior by way of a 

 terminal bladder. The special structure peculiar to leeches is a 

 capsule containing amoebocytes which is inserted between the 

 funnel and the tubular region. The capsule is small with a single 

 funnel in the primitive Glossiphoniidae but large with multiple 

 funnels in the Hirudidae. The Erpobdellidae have two capsules 

 and funnels per nephridium. Two functions have been ascribed 

 to the capsule. One is to receive coelomic corpuscles loaded with 

 excretory products, the other is to act as a site for the multiplication 

 of coelomic corpuscles. In primitive leeches such as Theromyzon 

 there is a communication between the cavity of the capsule and 

 that of the tubules (Fig. 24), so it is not difficult to see that 

 amoebocytes loaded with excretory products could break them 

 down and discharge them into the nephridium, but in most other 

 leeches there is a partition between the capsule and the rest of the 

 nephridium, and waste products must either diffuse through the 

 intervening tissue or travel via the coelomic circulation. Under 

 these conditions it seems that the capsule has changed its function 

 and become specialized for manufacturing coelomic corpuscles. 



