229 





c 



müde of termination of these canals, but it was known to all who 

 chose to trace them in transparent forms, that the canals become 

 exceedingly fine and probably in some cases ended in a netAvork of 

 spaces between the tissue-elements of the parenchyma of the body. 

 I certainly never believed in the abrupt termination which Van Be- 

 ne den has drawn for me (and I do not know who did), — but I in- 

 ferred the existence of an arrangement such as is shewn in the wood- 

 cut I now submit (C) . 



Van Beneden wishes to limit my reference to » channellings in 

 the mesoblast, sometimes spoken of as water- vascular system«, to the 

 larger trunks of the nephridia 

 which were certainly and defini- 

 tely figured and described as 

 the , excretory canals' or , water- 

 vascular canals' by the helmin- 

 thologists of thirty years since. 

 He declares that I must have 

 meant these canals and these 

 only and so could not have 

 conceived of such an arrange- 

 ment asFraipont has demon- 

 strated, namely — the continua- 

 tion of these , water- vascular canals' into a system of fine intercellular 

 spaces. 



M. Van Beneden 's contention would be defensible, had I not 

 in my essay on the , Primitive Cell-layers of the Embryo' carefully 

 explained that I held (as the diagram C shews) that the ultimate bran- 

 ches of the so-called water-vascular system form a system of lacunae or 

 network of spaces surrounding the tissue elements of the parenchy- 

 matous body. 



This fact — which seems to be the chief fact now remaining 

 among those originally overlooked byM. Van Beneden — is estab- 

 lished by the following extracts from the , Primitive Cell-layers '. 

 Ann. and Mag. Nat. Hist. 1873. p. 331 et seq. 



\^^ »In all Triploblastica it (the blood-lymph system) is represen- 

 ted by lacunae or channels or by mere wide-setting ofthe cel- 

 lular elements of the mesoblast, between and around which 

 the movement of a fluid, so-called lymph, is possible. A blood-lymph 

 system appears in its simplest form in the Flat-worms where the main 

 portion of those channellings in the mesoblast, sometimes spoken of as 

 , water- vascular system' must be regarded as the commencing diffe- 

 rentiation ofthe blood-lymph vascular system.« 



10** 



