No. 3.] THE DISCODRILID NEPHRIDIUM. 335 



have been distinguished a number of successive regions, most 

 of which will be found to present structural peculiarities. To 

 recapitulate, these regions are the funnel and its stalk, the 

 plexus region, with its alternating plexus nodules and simple 

 tubules, its main and accessory lobes, the outer and inner (or 

 recurrent) limbs of the longer tubule loop, the connecting tubule, 

 the outer and inner limbs of the shorter tubule loop, the efferent 

 duct with its connecting, coelomic, and intermuscular sections, 

 leading to a terminal vesicle. Were this entire tubule extended 

 it would have in a moderate-sized worm (3 mm. long) an esti- 

 mated length of 7 mm., or more than twice the length of the 

 entire animal. This would be distributed among the several 

 regions as follows : funnel and stalk, . i mm. ; plexus region, 

 2 mm. ; longer tubule (complete), 2 mm. ; connecting tubule, 

 .4 mm.; shorter tubule loop, i mm.; efferent duct, connecting 

 section, .5 mm.; coelomic, .4mm.; intermuscular, .6 mm. For 

 its entire length the tubule presents a fairly uniform diameter, 

 with, however, about twenty bead-like enlargements in the 

 plexus region and a less conspicuous one uniting the coelomic 

 and intermuscular efferent ducts. The tubule of the nephridium 

 shown in Fig. i, taken from a worm of 3^^ mm. in length, 

 measured nearly 9 mm. in the course of its windings. 



3. The Funnel. 



Each of the four nephridia is provided with an open ciliated 

 funnel, which, although of large size, is, owing to its transpar- 

 ency, rather inconspicuous. Its position is similar in all of the 

 species. That of the anterior nephridium is suspended by its 

 slender stalk from the extreme postero-ventral margin of the 

 plexus mass, and rather from its external than its mesial face. 

 Its obliquely truncate nephrostomal end usually faces ventrally, 

 internally, and posteriorly, and nearly touches the body-floor. 

 Its position may, however, be slightly shifted. The funnel 

 does not stand out freely, as represented in Dorner's figure (nor 

 is its position in American forms as there shown), but its base 

 and stalk are closely embraced by folds of the efferent duct, as 

 shown for several species in Figs, i, 6, 9, and 10, and in B. 



