46 THE LEECH 



place it on a slide in a drop of salt solution, and spread it out 

 with needles so as to show the mutual relations of its several 

 parts. 



Remove another nephridium in the same tuay, and tease it 

 slightly. 



Cover the specimens and examine with low and high 

 powers. 



a. The testis-lobe consists of a spongy mass of cells, 



traversed in an irregular manner by ductules. 



b. The main lobe consists of large finely granular 



cells, traversed in a very complicated manner by 

 fine branching ductules which pass across from 

 cell to cell, and are lined by a cuticular layer 

 continuous with that covering the exterior of the 

 cells. 



c. The apical lobe consists of cells traversed by much 



larger ductules, most of the cells being merely 

 hollow cylinders placed end to end to form tubes. 



d. The main duct of the gland is also formed of cylin- 



drical cells placed end to end, the passage being 

 intracellular. It commences at the apex of the 

 apical lobe, passes back along this lobe and along 

 the posterior and anterior limbs of the main 

 lobe, enters the apical lobe again, and goes right 

 round the loop a second time, and then passes 

 as the vesicle-duct to the vesicle. 



e. The vesicle, which is extremely dilatable, possesses 



a muscular coat, and is lined by a ciliated epithe- 

 lium, as is also the short passage leading from it 

 to the exterior. 



f. The blood-vessels form a very fine capillary plexus 



lying between the individual cells of the nephri- 

 dium. 



3. Special characters of the nephridia, 



a, The nephridia in the second to the seventh somites, 

 in which there are no testes, have the testis-lobe 

 short or absent, and devoid of the cauliflower- 



