230 



Thus the , wide-setting (i.e. set so as to leave intercellular spaces) 

 of cellular elements' is pointed out as a simple form of blood-lymph 

 system and immediately afterwards it is stated that the main part of the 

 canal -system of Flat -worms is a commencing blood -lymph sy- 

 stem. Surely this does not mean that the canal-system consists only 

 of comparatively large trunks which terminate blindly ! II means that 

 the larger trunks are continued into an inter-cellular system of spaces. 



2"'' This is further shewn by the reference which follows to Mr. 

 Mo s eie y 's researches on 13ipalium, — researches which by a very 

 natural coincidence M. Frai pont also cites in support of his views. 

 Speaking of M. M o s e 1 e y 's sections of Bipalium I say »The channels of 

 the water vascular system in these cases are seen in section to be inter- 

 sected by long branching cells; they are, in fact, only partial excava- 

 tions of the mesoblastic tissue. Such excavation, carried to a greater 

 extent and widened out, ultimately forms the perivisceral space seen 

 in many Nemerteans, and in all the Gephyrea, Chaetopoda, Echino- 

 dermata.« 



S'"^ In the following paragraph, I draw a parallel between the 

 flattened transparent Mollusc PhylUrhoë and the Flat-worms. It was 

 generally admitted that the blood-lymph space in the Mollusca is in the 

 condition of a series of inter-cellular lacunae assuming in some regions 

 the form of canals, — I could hardly have more distinctly stated my view 

 that the finer ramifications of the canal- system of the Flat- worms are 

 intercellular and not parts of the nephridia than by comparing 

 them to the blood-lymph system of a Mollusc. Yet M. Fraipont 

 erroneously stated that I considered these ultimate ramifications of the 

 canal-system of Flat-worms to be in tra- cellular and part of the 

 Nephridia, and M. Van Beneden has emphatically reiterated 

 this erroneous statement. My words are (loc. cit. p. 333). »In Phylli- 

 rhoë we have, it seems to me, as in the Flat- worms, the imperfect 

 channellings and spaces of a parenchymatous body placed in relation 

 with the exterior by the segment-organ, the wall of which is not dis- 

 continuous with that of the channels.« 



I may state once again, what I have previously admitted, namely 

 that I was unable to draw the line in the Flat-worms between the 

 ultimate ramifications of the canal-system which represent body cavity 

 and are intercellular and the terminations of the branches of the ne- 

 phridia or segment-organs. That was done when Buts ch li descri- 

 bed the ciliated lappets on the canals of Cercaria, and I have already 

 admitted that his observations and those of Fraipont have shewn 

 that the nephridial portion of the canal system extended somewhat 



