SEA-FISHERIES LABORATORY. 109 



origin from the lateral ami posterior margins of the 

 ganglionic mass, and these run outwards and backwards 

 as the lateral nerve cords. At intervals branches proceed 

 from them into the tissues of the suckers. They are 

 elliptical in section and can be traced backwards tis far as 

 the beginning of the appendix. Four other nerves take 

 origin from the anterior part of the central mass and these 

 (which are shewn in section, but not lettered, in fig. 5) 

 run backwards in pairs between the proboscis sheaths. 

 They become applied to the outer surfaces of the proboscis 

 bulbs and cannot be traced further. They are the 

 proboscidial nerves. 



Distinct regions are indicated in the central nervous 

 mass, thus the anterior sections contain the ganglion 

 cells, while the posterior ones display only neuroglial 

 tissues. The number of ganglion cells is quite small, all 

 could easily be reproduced in a plastic reconstruction of 

 the sections. The axial part of the mass appears to be 

 homogeneous, but the lateral parts appear to be differen- 

 tiated to form tracts running outwards towards the 

 various nerve roots. The proboscidial nerve roots can 

 easily be traced through the posterior sections of the mass 

 into the ganglionic regions. 



The posterior regions of the mass consist mainly of a 

 tissue which is certainly parenchymal in nature, and a 

 part of this is represented in fig. 4, PI. I. I liave 

 chosen a part which contains a ganglion cell. There is, 

 first of all, a framework of relatively coarse fibres or 

 trabeculae, bounding (in section) roughly polygonal 

 spaces. Filling this is the parenchyma, a tissue which 

 in sections appears to be a reticulum, but which, no 

 doubt, consists of homogeneous films meeting together so 

 as to include polyhedral spaces. In the preparations we 

 see, of course, mainly the sections of these films. Coarse 



