NERVOUS SYSTEM 



287 



(Fig. 70, Nv. 1*\) 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- 



/ 





JJer 



i ner.Epthm 



FIG. 70. Diagram illustrating the relations of the nervous system ui 

 Polygordius. 



The cleric epithelium (Da: Epthni) is either indirect contact with the 

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

 nerves (af. nv.) with the inter-muscular plexus (////. muse, plex.} : the 

 latter is connected to the muscle-plates (J/. PI) by efferent nerves (Ef. 

 nv). 



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

 nerve-cells (Av. C) : other nerve-cells (A T v. C') occur at intervals in 

 the inter-muscular plexus. 



The muscle-plates (Jlf. 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 (mi), to which the efferent nerves can be 

 traced. (The details copied from Fraipont.) 



diate contact with the deric epithelium. In the posterior 

 lobe of the brain the nerve-cells are superficial and the 

 central part of the organ is formed of a finely punctate 

 substance in which neither cells nor fibres can be made 

 out. 



