288 OTT. [Vol. VII. 



By careful focusing upon the living worm the water vascular 

 tube may be seen to run dorsal to the commissure. No trace of 

 a double commissure can be seen in sections, while in cross-sec- 

 tions of the worm the sections of the water vascular tube may 

 be seen to lie dorsal to the sections of the commissure. 



Bohmig ('90, p. 252) finds that the multipolar cells of the 

 brain of Plagiostomidae have from three to five processes, and 

 in opposition to Fridtjof Nansen, who says that a general con- 

 nection between the ganglion cells is not acceptable, states that 

 the cells are connected by these processes. 



Bohmig ('90, p. 254), in speaking of the material making up 

 the central nerve mass and the commissures of the brains of 

 Rhabdocoels, says that in sections under a high magnification 

 it can be resolved into a fine network. The meshes of this 

 network are very fine and are thickened in many places by 

 minute swellings. He agrees with Rawitz (^^6) and Leydig 

 ('85) in thinking that this network is present and that the 

 minute swellings are due to the crossing of the fibres of the 

 network. He says ('90, p. 253), "Die Fasern und Fibrillen 

 dieser nervosen Substanz bilden ein Netzwerk, sie anastomosiren 

 mit einander." 



According to Bohmig ('90, p. 254) Nansen says that the tubes 

 and fibrillae forming the Punctsubstanz do not anastomose with 

 each other. He says that the appearance of a network obtained 

 in cross-sections is not a network, but the cross-sections of 

 numerous tubes. 



Bohmig ('90, p. 256) says that Rohde (^6) thinks that the 

 finely granular material between the meshes of the network in 

 Polychaets is food material for the nutrition of the nerve fibres 

 composing the network and for the ganglion cells, while Leydig 

 ('85) and Nansen think it is the "true nerve substance." 



As before stated, it may be seen in sections which have been 

 treated by Kolliker's silver nitrate method that the ganglion 

 cells with their processes take a stain identical with that taken 

 by the fibres composing the apparent network of the commissure. 

 I was unable in any case to trace a distinct connection between 

 an individual fibre of the commissure and an individual cell 

 process, but in one instance it was possible to see a bundle of 

 nearly parallel fibres standing in such a relation to a group of 

 ganglion cells that they could hardly be interpreted otherwise 



