THE NEPHRIDIA OF LEECHES. 563 



sine as carefully as Schultze has done_, but all my observa- 

 tions tend to confirm those of that author. M. Bolsius finds 

 the recurrence of the duct a ''genetic*^ impossibility. I did not 

 overlook the difficulty, which is more real here than in 

 Hirudo, as will be seen from the following paragraph. 



"Except, perhaps, in the region of the funnel, and from the 

 vesicle to the exterior (the latter portion possibly an epiblastic 

 invagination), the lumen is contained in a perforated cell, and 

 is continuous throughout. In some regions the cell so per- 

 forated contains a network of finer ductules, which open 

 within the cell into the duct, e. g. in Clepsine (fig. 6 of b^) 

 and in Hirudo (fig. 7 of b, c, d). In other regions the cell 

 resembles a drain-pipe. At certain spots the duct in this 

 latter condition re-enters a mass of cells, as in Hirudo (fig. 7, 

 d), or even appears to re-enter a single cell, as in Clepsine 

 (fig. 6, e). With regard to this latter condition, I may point 

 out that numerous nuclei have been described in cells so re- 

 entered, and they may represeut groups of cells fused together. 

 It is a point needing further investigation.^' 



M. Bolsius has observed, at any rate, two nuclei in a " cell ; " 

 and I am surprised that, as a professed cytologist, he has not 

 paid more attention to the matter (especially when none of 

 the cells in Hirudo possess more than one nucleus), and has not 

 tested my suggestion, before fiatly denying the assertions of 

 Leydig, Gegenbauer, Whitman, Lang, Schultze, Yejdovsky, 

 myself, and others, as to the presence of a single continuous 

 duct. My hypothesis as to cell fusions must be tested by 

 careful embryological work; but I may add that in all the 

 teased preparations I have recently examined I have found 

 one nucleus in all cells perforated by one duct, two nuclei 

 in all *' cells" perforated by two ducts, and three nuclei in all 

 " cells" perforated by three ducts. My observations have, how- 

 ever, not been sufficiently numerous to enable me to lay down 

 a law in this matter. My diagram (woodcut, Clepsine, a, b) 

 and its description and the reference to it in the text are, I 

 admit, bad ; the three ducts, one branched and the other two 

 ' These references refer to the woodcuts here reproduced. 



