THE NEPHRIDTA OP LEECHES. 555 



I assert, no shadow of doubt but that it is so— that the duct 

 which is about to run to the vesicle runs along in the an- 

 terior limb of the main lobe towards the vesicle in a direction 

 opposite to the course of the organ itself as defined above, all 

 doubt that a portion of the duct may be recurrent disappears. 

 To return to the lobes. I have re-examined their arrange- 

 ment, both by means of sections and whole nephridia, both 

 fresh and after maceration for twenty-four hours in 10 per cent. 

 nitric acid, and have not the slightest doubt but that my pre- 

 vious account was correct. I cannot understand how M, 

 Bolsius can have failed to notice that in the posterior limb of 

 the horseshoe the main lobe, with its cells perforated by fine 

 arborescent ductules, comes suddenly to an end. In specimens 

 macerated in nitric acid it is easy to separate the recurrent 

 lobe from the main lobe, and to see that it, and not the end of 

 the main lobe, is continuous with the apical lobe. 



Then, so far as the duct is concerned, that there are two 

 ducts running through the anterior limb of the main lobe I 

 have often seen in fresh nephridia ; and in three separate series 

 of sections I have traced to my entire satisfaction the vesical 

 duct entering and running through the main lobe, leaving it to 

 enter the apical lobe near ^ (woodcut, Hirudo), passing along 

 the apical lobe round the apex and then coming out from the 

 lobe and running for some distance as a separate duct, then 

 plunging once more into the main lobe near where it first 

 entered that lobe, passing along the anterior limb and along 

 the recurrent lobe to the apical lobe. Of so much of its 

 course I am quite convinced ; that it passes as a duct along 

 the apical lobe again to the point g I am nearly sure, but its 

 walls become here so excessively thin that it is difficult to 

 trace it with absolute certainty. I shall, however, assume 

 that my impression is correct, and that it passes as a duct to 

 g. There it certainly communicates with the ductules. 



The ductules present more difficulty. They possess well- 

 marked characters in different parts of the organ. The 

 ductules in the testis lobe, those in the greater portion of the 

 main lobe, and those in the apical lobe are all very different 



