TYPE ANNELIDA. 235 



ture, since they differ from the sensory papillae only in the 

 greater number of the large vacuolated cells and in the pres- 

 ence of a quantity of black pigment in the surrounding tissues. 



Other sense-organs somewhat beaker-shaped in character 

 are found upon the prostomium and have been regarded as 

 gustatory in function. 



Nephridia occur in a number of the metaineres of the 

 middle portion of the body, there being in Hirudo (Fig. 108, n) 

 and its allies seventeen pairs. Each nephridium has a ter- 

 minal funnel, which in Clepsine has the typical Annelidan 

 structure, but in Hirudo has been modified so that the inner 

 extremity of each nephridium is constituted by a lobed spongy 

 ciliated mass without any definite central lumen. The funnel 

 lies in a blood-sinus, either the ventral one as in Clepsine 

 (Fig. 107, B] or the dorsal as in PontoMella, or in a sinus 

 which surrounds the testes as in Hirudo (Fig. 107, A), or in 

 a special sinus which is to be regarded as a ccelomic space as 

 in Nephelis (Fig. 107, 0). The canal which traverses each 

 nephridium is intracellular as in the Oligochneta, and in some 

 forms minute canals traverse the substance of each cell, open- 

 ing into the central lumen. As a rule the various nephridia 

 are quite separate and distinct from each other, but in Pontob- 

 della and one or two other genera they unite to form a net- 

 work of intracellular canals traversing several metameres. 

 Immediately before their exit to the exterior the canals 

 enlarge in some forms to bladder-like vesicles, from which 

 a short tube leads to the exterior, the opening being situated 

 either upon the anterior (Clepsine) or the posterior (Hirudo) 

 ring of the metamere to which the nephridia belong. 



The reproductive organs differ from those of the Chasto- 

 poda in possessing ducts which do not seem to be modified 

 nephridia and which are continuous with the walls of the 

 ovaries or testes. All the Hirudiuea are hermaphroditic. 

 The ovaries constitute in Clepsine two elongated organs which 

 lie in the middle region of the body, extending through several 

 metameres, but in Hirudo (Fig. 108, ov) they are small oval 

 or spherical bodies ; their ducts dilate to form a uterus and 

 finally unite to open on the inid-ventral line usually in the 

 eleventh metamere (Fig. 106, /o). The testes (Fig. 108, te) 



