ON THE ANATOMY 0¥ HISTRIOBDELLA HOMAEl. 301 



portion. It reaches its greatest length in the case of the 

 second nephridium (fig. 14). Frequently the lumen can be 

 seen to be enlarged into small spaces or lacunae. These would 

 seem similar to the spaces I have described on the nephridial 

 canals of Dinophilus. A number of these are usually seen 

 on the course of the second organ (fig. 6). One large one is- 

 often found on the posterior part of the third. From the 

 terminal portion of the canal they seem to be absent. The 

 nephridial flagella pass through their centre while their walls 

 themselves are unciliated. It is possible they are due to the 

 somewhat abnorma,! conditions under which the parasites are 

 kept in the process of their impi-egnation with methyl-blue^ 

 as I have never been able to observe their presence in the 

 unstained living Histriobdellay although something like 

 their appearance can be detected in sections. 



The terminal portion of the nephridial canal turns towards 

 the median line, close to which it ends in a darkly staining 

 pore (fig. 14). About this the blue usually collects in thick 

 granules^ which can sometimes be seen vibrating to and fro 

 in the fluid escaping from the canal. The lumen of this- 

 terminal portion is greatly restricted in size. 



Throughout the length of the nephridial canal the ciliary 

 action of the flagella in their interior can be plainly observed 

 during life. The movement of this is ahvays in the one 

 direction — from before backwai'ds — and I have never observed 

 any reversal of this motion as Haswell has described in 

 Stratiodriius. Despite numerous observations, I have 

 been unable to detei-mine whether the flagella are derived 

 from the walls of the canal or from the knob-like head of the 

 organ. In some preparations they seemed derived from the 

 wall, in others they seemed derived from the nephridial 

 heads. In sections they would seem to be derived from the 

 walls. 



■ In no case can the canals be seen dividing, as Haswell has 

 desci'ibed in the case of the first pair in the male of 

 Stratiodriius. I am quite positive in saying no su€h 

 division takes place in Histriobdella. They run through 



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