PERIPHERAL NERVOUS SYSTEM 



283 



the ventral cord appearing in sections (Fig. 69, c, and Fig. 

 72, A) as a mere thickening of the latter. 



Both brain and cord are composed of delicate nerve-fibres 



Drr 



aer. Ep th m- 



FIG. 71. Diagram illustrating the relations of the nervous system of 

 Polygordius. 



The deric epithelium (Der. Epthm} is either in direct contact with the 

 central nervous system (lower part of figure), or is connected by afferent 

 nerves (af. nv.} with the inter-muscular plexus (int. muse, pi ex.} : the 

 latter is connected to the muscle-plates (M. PI] by efferent nerves (Ef. 

 nv). 



The central nervous system consists of nerve-fibres (Nv. F) and 

 nerve-cells (Nv. C) : other nerve-cells (Nv. C') occur at intervals in 

 the inter-muscular plexus. 



The muscle-plates (M. PI], one of which is entire, while only the 

 middle part of the other is shown, are invested by a delicate protoplasmic 

 network, containing nuclei (), to which the efferent nerves can be 

 traced. (The details copied from Fraipont.) 



(Fig. 71, Nv. F.} interspersed with nerve-cells (Nv. C.}. In 

 the cord the fibres are arranged longitudinally, and the 

 nerve-cells are ventral in position forming a layer in imme- 



