386 



two parallel ducts are not exactly similar; the ductules around the 

 direct section are larger than those surrounding the recurrent part. 

 His fig. 1, A — B, reprinted in his critical paper, very clearly shows 

 that the main lobe is divided into two different parts, each of which 

 belongs to two different sections of the tube. In fact there is connec- 

 tive tissue between the two united sheaths of the parallel sections. 



Mr. Bourne did not remark it, as it was scarcely possible to 

 do with the method he prefers. In his critical article he makes a 

 rather compromising confession : "I am still in doubt", he says , " as 

 "to whether the ductules in the cells of the main lobe enveloping 

 " the duct near A (woodcut, H i r u d o) are in direct communication 

 " with those of the cells enveloping the other duct running parallel to 

 "it, viz. the duct near B; the former are larger and less branched 

 "than the latter, still I believe that communications exist" 

 (1. c. p. 556). 



That is to say that he had not seen the communication he 

 boldly draws in his fig. 1, A — B going from a cell belonging to the 

 sheath of the direct duct to another cell belonging to the sheath of 

 the recurrent duct. 



Authors ought not to draw details they have not seen; I never 

 draw what I simply believe to exist, knowing that an apparently 

 insignificant detail may have a great and unlooked-for importance. 



Now let us suppose that there is no connective tissue between 

 the two parts in connection and that there is real fusion between 

 the two sheaths and actual communication between the two systems 

 of ductules. Even then it would still be rational to consider the 

 main and the apical lobes as resulting from a secondary union of 

 two different sections of the duct with its sheaths of cells. 



All this being pointed out the reader will easily allow that my 

 fig. 3, as well as the sketch of Carl Vogt and Yung, may be ac- 

 cepted as a greatly simplified diagram of the general structure of the 

 nephridium. Without approving or disapproving, for the present, 

 Mr. Bourne's diagram, I think, I could strictly have accepted it, as 

 concerns the outer lines, with the condition of correcting the inner 

 structure as I have done in fig. 2, where the main and apical lobes 

 show the real disposition of the tube, Mr. Bourne's mistakes or 

 want of explanation being corrected. 



However, — I insist upon this, — I give that modification of 

 Mr. Bourne's diagram only with the view of clearly explaining my 

 view, without any possible ambiguity, and, as I have said, not at all 

 as if I had carefully verified it and found it exact in everything. 



