130 



WESLEY R. COE. 



Nerve cord muscle. In the genera belonging to the families 

 Arinaueriida: and Pclagoncmertida and in Pendonemertes of the 

 Protopelagonemertidce a narrow band of muscular fibers splits off 

 from the proboscis sheath on each side of the body immediately 

 back of the brain and extends backward throughout the length of 

 the body in close connection with the lateral nerve cord. In some 

 forms it lies close against the outer connective sheath on the 

 median face of the nerve cord, while in other cases it penetrates 

 the sheath and comes to lie in close connection with the nervous 

 tissues. This muscle is usually very thin, consisting of only one 

 or two layers of muscular fibers (Figs. 7, 8A), but in a few species 

 it is so large that it equals fully half the diameter of the nerve 

 cord itself (Fig. 8). 



In Pelagonemertes joubini the muscle leaves the proboscis 

 sheath as several separate strands (Fig. 7) and these may at first 

 take separate positions on the face of the nerve cord, but further 

 back in the body they fuse into a single flattened bundle. 



The function of the nerve cord muscle is evidently to hold the 

 nerve cord in position with reference to the organs which the 

 latter innervates. 



Peripheral nerves. As a rule three peripheral nerves leave 

 each lateral nerve cord in each of the spaces between adjacent 

 intestinal diverticula. One of these three nerves, dorsal peri- 

 pheral, leaves the dorsal side of the cord (Figs, i, 2, 7, 8) to 

 supply the dorsal musculature and integument and in some cases 

 the proboscis sheath (Figs. 2, 7). This nerve also sends branches 

 into the intermuscular plexus and indirectly connects with the 

 dorsal and dorsolateral nerves. Small branches also supply many 

 of the dorsoventral muscles. 



The lateral peripheral is a slender nerve with few branches. 

 These supply the lateral margin of the body and appear also to 

 enter the intermuscular plexus (Figs. 2, 7). 



The ventral peripheral originates from the ventral core of the 

 cord and divides into two branches which supply the ventral 

 portions of the body. Branches from this nerve also enter the 

 ventral intermuscular plexus (Figs, i, 2, 7, 8). 



Intermuscular plexus. In some of the sections of Ncurone- 

 mertes aurantiaca distinct nerves can be seen leading from the 



