CONTEIBUTIONS TO THE ANATOMY OF THE HIRUDINEA. 425 



2. Internal. — The first annulus (fig. 8.) (i) lodges the 

 nerve-ganglion of the somite {gn.). The funnel of the nephri- 

 dium {neph.fun.) lies in the posterior portion of the annulus. 

 The testis [t.) lies in the region of annulus iii. 



The dissepiments figured by Vaillant have not the importance 

 which he attaches to them; they are the groups of dorso- 

 ventral muscles, and occur three or four to every somite rather 

 than as he has figured them. 



The anterior sucker (figs. 1 and 2, a.) may be regarded 

 as prostomial fused probably with the first annulus of somite 

 1, following this come the other three annuli of this somite 

 and then, successively, three complete somites (2, 3, and 4), 

 the first and only annulus of somite 5, the cliteilum (somites 

 6 and 7), and then 13 somites (8 — 20) in front of the anus, 

 making 20 well-marked somites. Somites 19 and 20 are much 

 reduced, presenting only two annuli each. The region lodging 

 the anus represents several somites, which were probably 

 present in an ancestor, but are now completely obliterated. 



Thus, the somites at the anterior and posterior portions of 

 the body and the clitellar somites become more or less reduced 

 and fused. 



The cliteilum (fig. 7.) presents at either extremity a small 

 ring devoid of papilla3 {a, b), possibly with some special relation 

 to the formation of the cocoon. 



The first annulus of the first clitellar somite presents eight 

 papillae with an arraugemeut difl'eriug but little from that 

 obtaining in annulus i of an ordinary somite. 



The second annulus presents six larger papillae and two 

 smaller. Between these two annuli is lodged the male genera- 

 tive pore [g. p., ^), which is transversely oval with protrud- 

 ing lips. 



The posterior clitellar somite presents an almost exact repe- 

 tition of this arrangement, the female generative pore {g. p., ? ) 

 being lodged between the two annuli and being rather smaller 

 than the male pore. 



An examination of fig. 3 will show that a similar con- 

 densation of the internal organisation takes place in this region 



