58 THE LEECH. 



slide in a drop of salt solution, and examine with low and high 

 powers. 



The entire nephridium consists of the following 

 parts : 



a. The testis-lobe forms the ventral half of the anterior 



limb of the loop. It is a cylindrical rod, the 

 inner end of which lies' in the peri-nephrostomial 

 sinus on the dorsal surface of the testis. This 

 end is slightly enlarged, and has a cauliflower- 

 like appearance, the cells covering it being spongy 

 and ciliated, and often depressed at their ends. 



This inner end of the testis-lobe probably 

 corresponds to the funnel-like opening of the 

 nephridium into the body-cavity in the earth- 

 worm (p. 27). 



b. The main lobe is the thickest part of the rod : it is 



continuous with the outer end of the testis-lobe, 

 and forms the anterior limb, the bend, and half 

 of the posterior limb of the loop. 



c. The apical lobe is separated by a slight constriction 



from the posterior limb of the main lobe. It runs 

 downwards and inwards, diminishing slightly in 

 thickness, and 'ends in a coiled-up extremity, the 

 apex of which is closely attached to the junction 

 of the testis-lobe and the main lobe. 



d. The vesicle-duct is a short narrow tube arising 



from the anterior limb of the main lobe at its 

 junction with the testis-lobe, and running back- 

 wards beneath the apical lobe to the vesicle. 



e. The vesicle is a somewhat flattened sac with 



muscular walls : it lies behind the rest of the 

 nephridium, and opens to the exterior by a short 

 duct, the opening being on the ventral surface of 

 the body and in the hindmost annulus of the 

 somite in which the nephridium lies. 



D. The Reproductive System. 



Leeches are hermaphrodite, but do not impregnate their 

 own ova. 



