316 WILLIAM A. HASWELL. 



tiuctly differentiated ; a comparison of my figures of trans- 

 verse sections with those of Foettinger will show how marked 

 this difference is. 



There are no organs of special sense^ unless we reckon as 

 such the tentacles and cirri ; there are no vestiges of eyes, 

 and the ciliated pits described by Foettinger as occurring in 

 Histriobdella are not present. 



Excretory System. 



The excretory organs (fig. 1) take the form of a series of 

 pairs of ciliated canals. These are for the most part very 

 thin-walled, so that they are only to be traced in the living 

 animal by the movement of the cilia, and are not to be 

 followed with any certainty in any of my series of sections, 

 except in one or two localities where their walls are thicker. 

 A good many details thus remain to be elucidated, but 

 the following general features have been satisfactorily made 

 out. 



The arrangement of these canals differs considerably in the 

 two sexes. In both the system extends forwards into the 

 head, and backwards as far as the posterior end of the body. 

 Each nephridium of the most anterior pair divides in the 

 fii'st segment into an external and an internal branch. The 

 former runs right forwards into the head. The latter crosses 

 obliquely over to the opposite side, and joins the external 

 branch of the opposite nephridium. Judging from the 

 direction of movement of the cilia, which is always from 

 behind forwards, the external apertures of this pair of 

 nephridia must be in the head. None of the other nephridia 

 are branched. In the female an apparently continuous line 

 of cilia is traceable backwards on each side from the head 

 canals to a point some little distance behind the second 

 cirrus, where a canal is clearly traceable, which, after bend- 

 ing round in a loop, opens on the exterior on the ventral 

 side. But as the direction of movement of the cilia is from 

 before backwards in the posterior part of this line, it would 



