390 



I shall not try to give a complete and adequate interpretation 

 of fig. 8 of Schultze. Let me simply remark that the portion D is 

 extraordinarily similar to the longest commisure, lc, of my fig. 6 and 7. 

 These appearences and others of the same kind, obtained with Mr. 

 Bourne's own methods have led me to the conviction that some of 

 the commissures — very short and separated by very small apertures — 

 have entirely escaped Schultze and Bourne; and that some others, 

 — very long, — have led both of them, especially the latter, to an 

 entirely erroneous view of the general structure of the organ, in 

 which too much attention is attached to the external form and too 

 little to the inner structure. 



Besides, whatever be the cause of these misunderstandings, I 

 maintain that the organ consists of a single row of cells perforated 

 by three separate canals, and, thus, very different from that of Hirudo. 

 The intracellular nature of all its cavities is the only feature common 

 to both. In fact this very important character is quite sufficient to 

 give a serious basis to the histological analogy of these undoubtedly 

 homologous organs; and there is no objection in the difference in the 

 number of canals and other secondary features, against the generally 

 accepted view of the affinities and relationship of the Hirudinids with 

 the other families of the same group of worms. 



Recapitulation. 

 To sum up: 



1. As regards the genus Hirudo, I maintain my previous de- 

 scriptions — including the diagram, fig. 3, insisting on the fact that 

 it is given as a greatly simplified schema of the unrolled organ. Had 

 Mr. Bourne rightly understood my several memoirs, he would have 

 discovered that the organ has always been supposed to be unrolled. 

 I hope he will now acknowledge that on this point there was between 

 us more misunderstanding than real disagreement, since I could to a 

 certain extent accept his own diagram with the condition of explaining 

 the inner structure as I have done and as he ought to have done him- 

 self long ago. 



2. As regards Nephelis, a discussion between us is hardly 

 possible. Mr. Bourne in its 1884 paper regards the segmental organ 

 of this animal as typically identical to that of Gnathobdellids. 

 In his critical paper he does not give up his former view, though in 

 contradiction with Ose. Schultze, Vejdovsky, and others. 



3. As regards the Clepsinids (Glossiphonids) there is real 

 disagreement between Mr. Bourne and myself; I also maintain my 

 views : 



