332 MOORE. [Vol. XIII. 



strong septum 'Vv> i^ contact with which they arch upward 

 over the intestine and cross to the right side, turning there 

 ventralward, and becoming attached to the body-walls. When 

 on the right side the tubules first pass dorsally over the opaque 

 mass, and transversely from right to left. 



The funnel and efferent duct are connected with the opaque 

 mass at nearly the same point, which is about opposite to the 

 place of origin of the tubule group. Keferstein (24) in Bran- 

 chiobdella, and the writer in Bdellodrilus, have traced the efferent 

 duct to its communication with the tubule loops. After leaving 

 the opaque mass the efferent ducts become conspicuous tubules 

 which pass transversely around the major annulus of the third 

 somite to open by separate dorsal pores (Branchiobdella), or 

 by a common median dorsal vesicle and pore (Bdellodrilus, 

 Pterodrilus). 



The post-genital pair of nephridia are confined to one seg- 

 ment, already largely occupied by the muscles of the sucker; 

 they are consequently less conspicuous than the anterior. They 

 lie in the eighth somite symmetrically^ on each side of the intes- 

 tine, and in B. instabilia extend into the flange-like lateral 

 flattenings of this region. As Henle (21), Dorner (14), and 

 Lemoine (25) have already mentioned, the posterior nephridia, 

 although obviously constructed on the same plan, are much 

 more irregularly arranged than the anterior, which results from 

 the necessity of the tubules to accommodate themselves to the 

 muscle fibres which traverse and divide the coelom. The 

 tubules are smaller and in many ways more difficult to study. 

 The granular mass is rather small and lies at about the middle 

 of the segment. The tubules are arranged in a U-shape around 

 it, the open end of the U forward, and away from the granular 

 mass. The outer limb is the shorter and the moi-e complex. 

 The six tubules which it contains may be traced as three which 

 arise from the mass, extend forward on its outer margin, and 

 return to pass around it to the inner side, continuing there as 

 the inner lobe, which receives a fourth tubule — the four being 

 then grouped into two loops which reach forward to the septum 

 ^"/viii- Ori comparison with an anterior nephridium it will be 



1 Lemoine states that in B. parasita the left is slightly in advance. 



