300 CRESSWELL SHEARER. 



of the body, Stratiodril us having the same number of 

 segments as Histriobdella. In no part of the canals were 

 ciliary flames observed. 



3. General Description op the Nkphhidia. 



From the inspection of figs. 1, 7, and 9, it will be seen that 

 the nephridia have much the same positions as those assigned 

 them by Foettinger (8). Apparently in the male the fourth 

 pair, figured by him in the genital region, have no existence. 

 Like the female, the male has only four pairs of organs. It 

 will be seen that they are the narrow, delicate, S- shaped 

 structures he has described (figs. 4, 5, 6, 10, 14), running in 

 the mesodermic tissue of the body-wall. Their position in 

 sections can be seen in figs. 37 and 43. Each organ takes its 

 origin in a small space — a prolongation or part of the 

 general blastocojlic cavity that surrounds the gut — in the 

 anterior portion of the segment to which it properly belongs, 

 and runs back to terminate on the ventral surface of the 

 following segment near the median line. It ai-ises in a knob- 

 like process that projects slightly into the space. This 

 process is thick-walled, and sometimes contains refractive 

 granules. It is shown in fig. 14. Its structure is difficult to 

 determine, and especially the relationship it bears to the 

 space. What I take to be the real head of the organ is 

 shown in section in fig. 42. Here the space into which it 

 projects is surrounded by darkly staining nuclei. These ai"e 

 not seen in the living condition. It bears no cells that have 

 any resemblance to solenocytes, and these structui'es would 

 seem to be entirely absent in Histriobdella. In a number 

 of preparations it was obvious that the internal ends of the 

 canals were closed, and that they did not open into the space 

 into which they project. 



The main portion of the nephridial canal is a thin-walled 

 intra-cellular tube, the anterior end of which contains a few 

 refractive granules and nuclei. It runs directly backwards 

 in an oblique plane^ and is much longer than the terminal 



