388 



In C 1 e p s i n e the nephridiura differs only from that of N e p h el i s 

 in the manner the cells are united. Instead of being stuck to each 

 other on a large surface as in Nephelis, they are united by two 

 or three bridges, each of which contains either one or sometimes two 

 ducts. These bridges vary greatly in size; some are very thick and 

 short; others are long and thin. 



The differences between Mr. Bourne's statement and my own 

 clearly appear in my diagram fig. 5 if compared in that of my op- 

 ponent's fig. 4. 



Let us remark that the organ in my diagram of Clepsine is 

 supposed to be entirely unrolled, as is also the case in fig. 3 relating 

 to Hirudo. 



The chief points on which I disagree with Mr. Bourne are the 

 following : 



1) There are three separate ducts, and not a single one coiled 

 up in such a way as to pass thrice through the same mass of cells. 



2) None of these three ducts is surrounded by a sheath of cells 

 with ramified ductules; the ductules where they are seen belong to 

 the peculiar duct-cells in which the three ducts end. 



Mr. Bourne's fig. 4, section A — B, is thus entirely erroneous. 

 The ducts have no special wall, I mean no other wall than that com- 

 posed of the cells they run through. 



Mr. Bourne seems here again to have been led astray by the 

 preconceived idea of an adequate analogy between the different genera 

 in question, and, as a consequence, to have admitted a priori the 

 existence, in the nephridium of Clepsine, of two distinct elements: 

 the wall-cell and the ductules-cell. The mass of ductules- 

 cells would then be homologous to the main lobe of Hirudo and 

 thrice traversed by the duct. But that is quite a mistake. 



In fact the duct-cell and the ductules-cell are distinctly existent 

 in Hirudo, and correspond to the central canal and to the sheath 

 of cells. But there is nothing like the sheath in Nephelis and 

 Clepsine. The wall-cells alone, set up in a single row and pierced 

 by the three ducts are present, and a few of them only contain ter- 

 minal ramifications. Had our opponent detected in his first works 

 the real structure of the duct-wall, he most probably would have 

 found out the superior ending of the three ducts and abandoned at 

 least for Clepsine and Nephelis his recurrent-duct-theory. 



In his critical paper however he makes a very important con- 

 cession. After a close re-examination of his preparations he arrives 

 at the following practical conclusion and frank confession: „My diagram 



