Structure of an Australian Land Leech. 231 



VI. The posterior nephridium (17th) lying in segment XXI T. 

 resembles in external appearance the majority of nephridia in 

 that it is less compact, but it is larger. The duct, however, from 

 the excretory vesicle passes back and opens on a small papilla-like 

 structure formed by the 78th and 79th annuli, so that is there is 

 no external opening in segment XXII. nor in segment XXIIl. 

 (represented by 97th annulus) but the orifice occurs on the 

 posterior edge of what represents segment XXIV. This modiH- 

 cation in the arrangement of the 17th nephridium may be 

 compared with that which takes place at the anterior end. 



Reproductive Organs. (Figs. E. and 2). 



The reproductive organs are situated in the middle region of 

 the body on the ventral side of the alimentary canal and above 

 the nerve cord. 



The male organs consist of ten pairs of testes arranged on both 

 sides of the nerve chain in segments XII.-XXI. inclusive. Each 

 testis lies in the second and third annuli of its segment and is 

 spherical in shape. The spermatzoa are developed in these in 

 regular masses as in other cases. 



Attached to the lower and outer edge of the testis is a mass or 

 botryoidal tissue. At the outer side of the testis sometimes from 

 its anterior, sometimes from its posterior margin, opens the v.vs 

 efferens, a small definite walled duct. Each of these vasa 

 eflferentia opens into the vas deferens of its own side, which runs 

 from the tenth pair of testes forwards as far as the twenty-sixth 

 annulus, that is about the level of the male external opening. 



The vas deferens remains up to this point of uniform size. 

 Here it turns, passing towards the posterior end (on the ventral 

 surface) and becomes exceedingly fine. About the region of 

 segment XII. it dilates into a very thick walled and much coiled 

 tube, which may be called the right or left epididymis. These 

 structures, continuous with their vasa deferentia lie in the middle 

 line dorsal to and about the level of the upper part of the vagina. 



The epididymis of the left side lies anterior to the right in tht; 

 middle line. 



