50 BRISTOL. [Vol. XV. 



I have found evidences of the intermuscular nerve ring in 

 this annulus, but I have not been able to trace them com- 

 pletely enough to describe the relations which the ring bears 

 to the other parts of the nervous system. 



The annuli lying in front of annulus 4 are incomplete, as 

 shown in PL VI, Figs. 5 and 6. Annulus 3 is well marked off 

 on the dorsal side, and the groove separating it from 2 is clear 

 and sharp in outline, while i is separated from 2 by a partial 

 groove extending about two-thirds of the way across the dorsal 

 surface. 



Nerve II innervates the numerous, large, dorsal sensillae of 

 annulus 2, a few small ones on annulus 3, and the large first 

 pair of eyes in annulus 2. The ventral branch of this nerve is 

 reduced to a small branch that traverses the long axis of the 

 first eye and proceeds to a few of the dorsal labial organs. 

 Annuli 3 and 2, therefore, make up metamere II, and the 

 nerves of this metamere, like those described, innervate the 

 preceding metamere. Nerve I innervates annulus i, supply- 

 ing the numerous large sensillae and the numerous mid-dorsal 

 labial organs. This fact raises the prostomium to the rank of 

 a metamere, and it must be counted as one. It has been cus- 

 tomary to disregard this reduced portion in numbering the 

 metameres and annuli, but hereafter it must be reckoned in 

 the count of metameres and annuli, as Whitman has done in 

 Clepsine (/. c). 



Thus far the external features of the sub-oesophageal ganglia 

 and the "brain " and the distribution of the nerves have been 

 analyzed with concordant results ; there remains an internal 

 factor that adds still further proof for Professor Whitman's 

 proposition. In Nephelis, as in Clepsine and other Hirudinea, 

 each body neuromere contains, as I have said, two " median 

 nerve cells." In Nephelis, as in Clepsine, they are found in 

 the sub-oesophageal portion, but arranged numerically, four 

 pairs appearing instead of five, as Whitman finds in Clepsine. 

 Careful examination of excellent sections reveals further that 

 in each side of the collar, near the capsules, 2.2., ascribed to 

 metamere II is a " median nerve cell " somewhat irregularly 

 compressed. The volume of the cell is still large, and the 



