No. 3.] THE DISCODRILID NEPHRIDIUM. 339 



this highly probable; likewise the presence of anastomoses 

 between the separate windings of the canal is uncertain." 

 Lemoine (25) follows Odier in retaining the name red gland, 

 and after a somewhat elaborate description of the shape, color 

 in various parts, and external relations, admits ignorance 

 regarding the internal structure. The presence of intra-cellular 

 plexuses in the yellow mass was indicated in my paper on the 

 Anatomy of Bdellodrilus illuminatus (28). 



As the constitution of the plexus region of this species is 

 such as to render it a more favorable object of study than the 

 others, the account can conveniently begin with a description 

 of it. If a nephridium, preferably the anterior one, be dissected 

 out entire,^ and examined while yet fresh in a drop of water, 

 the plexus region presents the appearance of a somewhat com- 

 pact and irregularly rounded, lobulated mass, from the surface 

 of which rounded nodules stand out here and there more promi- 

 nently. One is forcibly struck by the resemblance in form of 

 such a preparation to a bulbous-rooted plant. The plexus region 

 resembles the thickened subterranean parts, while the straight- 

 ened tubule loops with their outstanding leaf-like peritoneal 

 cells simulate the aerial stem. If now the granular mass be 

 subjected to the pressure of a cover glass, and the nodules 

 gently flattened, the plexus of canals will become very distinct 

 in certain of the marginal ones, while in nearly all of them it 

 becomes more or less clearly visible. The entire interior of 

 the highly granular substance of the plexus nodules is found 

 to be everywhere excavated by a system of branching and 

 anastomosing canals. These are very tortuous in their courses, 

 of very irregular diameter, and without any definite plan of 

 branching. The more superficial ones form irregular arches 

 and loops (Fig. 18), which frequently approach very close to the 

 surface, leaving only a thin shell of protoplasm. At two points 

 within each nodule the passages converge and unite. Most 

 frequently these points are close together (Fig. i,/;/), so that 



1 This operation can be performed much more readily upon B. illuminatus than 

 any other species, owing to the weakness of the muscular layers. In other species 

 the body muscles are so thick and strong that they cannot be torn asunder without 

 serious injury resulting to the delicate organs within. 



