387 



I wonder how Mr. Bourne can give so great an importance and 

 autonomy to the main and apical lobes, and how he can abstain 

 from any interpretation of the process of the genesis of these lobes, 

 the twofold nature of which clearly appears in sections like his 

 fig. 2, A— B. 



He seems to have been led to his views by the theoretical prin- 

 ciple that the nephridia must be similar in the Hirudinids and in 

 the other families, more than by the strict observation of facts; and, 

 having discovered a recurrent duct in one of them, he has been 

 easily induced to state what we may call the recurrent-duct-theory. 



Unfortunately I am obliged to differ from his opinion as regards 

 two genera of these families, viz: Clepsine (Glossiphonie) and 

 N e p h e 1 i s , still more widely than as regards the Hirudinids, the 

 nephridia of the former being much more different from those of 

 Hirudo than Mr. Bourne might believe. 



III. 



Nephelis and Clepsine. 



a) The nephridium of Clepsine, in Mr. Bourne's opinion 

 (fig. 4, Taf. V) is built up on the same plan as that of H i r u d o. In his 

 diagram it differs from the latter especially by the fact that the duct — al- 

 ways single and possessing a recurrent part — runs through only 

 one mass of cells, which corresponds to the main lobe of Hirudo. 



The cells which compose this lobe contain ramified ductules. 

 A testicular lobe, ending at the funnel, is annexed to the main lobe, 

 but is not traversed by the duct. 



b) To my mind, on the contrary, the segmental organ of Clep- 

 sine and Nephelis is greatly different from that of Hirudo. 

 The chief difference I have detected is that it consists only of a 

 single row of cells (fig. 5, Taf. IV) ; these cells form the wall of the duct 

 which is not surrounded by a sheath of other cells as it is in the 

 Hirudo. This row of cells, homologous to the drain-pipe of Hirudo, 

 without its sheath of cells, is not traversed by a single canal, but by 

 two or three different pipes, according to the regions. If followed 

 through the cell row each of these ducts may be seen resolving itself 

 in the upper part of the organ, into a bunch of tiny ramifications. 



It is quite certain that the three lumina found in certain 

 transverse sections do not belong to one single duct thrice coiled 

 up, but to three different ducts passing through one single row of 

 cells, and meeting only in the lower part of the organ. 



There is no continuity between the segmental gland and the 

 ciliated organ or funnel. 



