NERVOUS SYSTEM. INVEKTEBRA.TA. 7 



it shows no sign of metamerio ganglionation, but on a 

 level with each annular furrow gives off a delicate pair of 

 nerves. 



Neuropile* appears to be mainly confined to the cerebral 

 ganglion. The medulla of the cord consists of a dorsal 

 stnmd of nerve-fibres, covered on its ventral su'rface 

 by a continuous layer of unipolar ganglion-cells, mostly of 

 small size (fig. 3). At the point of union of the cord with 



Fig. 3. 



F. M. 



N.S. 



L.M. 



Transverse section through the Ventral Cord of Arenicola marina, x 50. 



C.M. Circular muscles. G.C. Ganglion - cells. G.F. Giant fibres. 

 L.M. Longitudinal muscles. M. Medulla. N.L. Neurileinnia. 

 N.S. Neuroglia septum. P. Peritoneum. 



the oesophageal connectives jmd on a level with the anterior 

 end of each setigerous segment, are a pair of giant ganglion- 

 cells. In several instances a direct connection has been 

 traced between these cells and three giant fibres that lie 

 along the dorsal aspect of the cord. The distribution of 

 the giant fibres is still doubtful. The cord is surrounded 

 by a neurilemma, and is permeated by a considerable 

 quantity of neuroglia fibres. These are specially concen- 

 trated in the sagittal plane, and form a partial septum 

 between the two halves of the cord. In the specimen the 

 general form and position of the cerebral ganglion, circum- 



oesophageal connectives, and ventral chain can be seen, but 



% 



* The felt-work formed by the ultimate ramifications of ganglion-cell 



professes. 



