No. 3.] THE DISCODRILID NEPHRIDIUM. 363 



efferent and recurrent tubules, and in which the lumen has 

 developed side branches. The corresponding tubule in this 

 region of Lumbricus also shows, according to Benham, slight 

 indications of branching. In both types the efferent duct 

 leaves the body of the nephridium at the same point at which 

 the nephrostomal tubule enters. The former in Clepsine is 

 direct, in Lumbricus looped and very wide, but this region is 

 highly variable in both groups which these two genera repre- 

 sent. The funnel of Clepsine is primitive, but open and func- 

 tional ; while the stalk, the testes lobe of Bourne, is highly 

 important, and differs from the main lobe only in that it is free 

 from the other tubules, and its cells smaller. Lumbricus has 

 a highly specialized funnel, while the stalk is a simple conduct- 

 ing tubule. 



The hirudinean meganephridium which departs most widely 

 from that of Clepsine is that of Hirudo and its allies on the one 

 hand, and Nephelis on the other ; in the former the funnel has 

 degenerated from a highly specialized condition, and its cavity 

 is occluded, which Bourne (11) notes is connected with an in- 

 creased richness of blood supply. The perforated cells of the 

 testes, main, and apical lobes no longer form a simple series, 

 but have increased to a number of rows, the lumen becoming 

 similarly divided to form a network, which is most complex in 

 the main lobe, where the recurrent and efferent tubules have 

 each acquired a special cellular sheath. The coecal lobe is also 

 a special addition to the nephridium of Hirudo. But the tubule 

 arrangement is exactly the same as in Clepsine, which serves 

 well as a type. The nephridia of Nephelis, as recently de- 

 scribed by Graf {Jen. Zeit., XXVIII, pp. 163-195) presents a 

 very simple arrangement in that the tubule, although sinuous 

 and folded in its course, nowhere becomes complicated by 

 recurrent or encircling loops. Although the lumen develops 

 lateral branches for a great part of the length of the tubule, 

 the plexus region is confined to a small nodule which is envel- 

 oped in a network of blood vessels. The funnel is functional. 

 In many respects this nephridium closely resembles that of 

 certain Tubificidae as described below, but most of these are 

 thrown into U-shaped loops. 



