284 W. B. BENHAM. 



very likely be merely a thickening of the body-wall. If it be 

 a prostate^ then Callidrilus, like the rest, will belong to 

 Eudrilidse; but even here it will form an exception to the 

 general characters of the family in the position of the clitellum, 

 and in the character of the nephridia and spermathecse. 



The chief point in which Pygmaeodrilus approaches 

 Eudrilus is in the possession of elongated prostates, and of a 

 penis within a '^ bursa." The muscular part of the sperm- 

 duct very probably corresponds to a portion of the prostate of 

 Eudrilus, in which the duct enters the prostate some distance 

 along its length. 



Polyto rentes and Stuhlmannia present so many ab- 

 normal characters that it is desirable that we should have more 

 detail before deciding on their affinities. Apparently they are 

 most nearly related to Teleudrilus. 



VII. Explanation of Diagrams. 



These diagrams, representing the genital, alimentary, and 

 excretory systems of the genera recognised in the accompany- 

 ing paper, have been constructed in most cases from drawings 

 published by the various authors mentioned below, or, where no 

 figures have been given, from the descriptions of the different 

 worms. I have usually selected those species which have been 

 most fully and most recently described, as types of the genera. It 

 must be borne in mind that the accompanying figures are merely 

 diagrams, and are not accurate copies from previous figures. 

 I have arranged them in the same order as that in which the 

 genera have been described in the body of the paper, and the 

 numbering of the figures agrees with the numbering of the 

 genera. 



In every case the clitellum, if it occurs within the first 

 twenty somites, is indicated by the thickened boundary of the 

 diagram. In all cases the upper figure {a) represents genital 

 system ; the middle (6), alimentary and excretory systems; the 

 lowermost figure (c), a few somites seen externally. 



In the diagrams of the genital system the testes and ovaries 

 are in black, the genital ducts in outline, the sperm-sacs and 



