12 



LEECHES 



The ovaries are elongated cords with club-shaped terminations 

 which lie freely in a single pair of coelomic sacs in segment XL 

 Short ducts run from these to a common oviduct, which is closely 

 invested with a thick layer of unicellular albumen glands. The 

 oviduct leads to a U-shaped muscular vagina which in turn opens 

 to the exterior. Ova are budded off from the cords in the ovisacs, 

 are fertilized by sperm received from another leech, and finally 

 coated with albumen in the oviduct. After the cocoon has been 

 formed by the clitellum the fertilized eggs are passed from the 

 female pore into the cocoon, which the leech then slips over its 

 head. 



5. Excretory System 



There are seventeen pairs of nephridia opening on segments 

 VII to XXIII. The parts of a typical nephridium are shown in 

 Fig. 5. The outstanding feature of this nephridium compared 

 with those of most other annelids is the complete separation of the 



Testis sac Vas deferens 



Initial lobe 



Inter -cellular duct 



Main lobe 



Intra -cellular 

 duct 



Vesicle 



Fig. 5. Details of a right nephridium as seen in situ when the 

 body wall has been pinned out as in Fig. 3(b). After Bhatia, 1938. 



funnel from the rest of the nephridium. It has become modified 

 almost out of recognition and has become functionally a part of 



