No. I.] THE METAMERISM OF NEPHELIS. 6l 



Summary. 



1. Nephelis differs from nearly all other leeches in the 

 external topography of the somite. The prominent sense 

 organs present in most genera are not easily visible in Nephelis, 

 excepting a few somites in the anal region. 



2. Color and color markings do not afford criteria for the 

 determination of specific characters. 



3. The body somites consist of five annuli as determined by 

 the nephridiopores. The somites of the terminal regions, contain- 

 ing less than five annuli were determined by the innervation. 



4. But one species of Nephelis came under my observation 

 though the collections were made over a wide area of country. 



5. The food supply is the controlling factor in the choice of 

 location in a pond or brook. 



6. The head region contains six somites ; the body region, 

 eighteen ; the anal, ten, making thirty-four in all. 



7. The anterior nerve of a body neuromere arises from two 

 roots which fuse quickly ; the anterior nerve is, therefore, the 

 morphological equivalent of the first and second nerves of 

 Clepsine, while the posterior nerve in Nephelis is the equiva- 

 lent of the posterior nerve in Clepsine. 



8. " Leydig's cell " is present in every neuromere from one 

 to thirty-four. 



9. The innervation of a body metamere in Nephelis is mor- 

 phologically identical with that of Clepsine. 



10. The three anterior neuromeres of the anal ganglia show 

 evidences that reduction in Nephelis has progressed by so 

 much more than Clepsine, whose anal ganglia are represented 

 by the succeeding seven neuromeres. In the head region the 

 number of neuromeres is the same in both. 



1 1. The distribution of the nerves in the somites of the ter- 

 minal regions is precisely referable to that of a body somite. 



12. In both terminal regions each neuromere contains every 

 element found in a body neuromere. 



13. A peripheral system of nerves composed of large bipolar 

 cells, which I have called intermuscular nerve rings, is in inti- 

 mate connection with the central system. 



