126 WESLEY R. COE. 



Dorsal nerve. This nerve appears to represent a local con- 

 centration of fibers from the dorsal peripheral nerves, for it is 

 not connected directly with the brain, so far as known, in any 

 of the pelagic forms. It extends in the median line and just ex- 

 ternal to the circular muscular layer, joining the commissure of 

 the lateral nerves at the posterior end of the body. When fol- 

 lowed forward toward the brain it becomes gradually smaller and 

 finally terminates in the cephalic parenchyma or in the delicate 

 intermuscular plexus a short distance posterior to the dorsal brain 

 commissure (Fig. i). 



Fibers from the dorsal nerve supply the dorsal musculature and 

 integument of the body. Other fibers enter the nervous plexus 

 lying between the two muscular layers, while still others are con- 

 nected with the dorsolateral and dorsal peripheral nerves. 



y v ^ s, v y 



-?-^~ ^^^ ^^ ^%&~ ^W^ ^T^" ^^sH^ 

 a 



FIG. 3. A, Diagram of anterior end of dorsal nerve with its accompany- 

 ing ganglia, showing variations in shape of the latter and the minute fibrils 

 which pass dorsally into the integument and ventrally into the intermuscular 

 plexus. B, Similar diagram from near middle of body. 



Ganglia of dorsal nerves. In most species only a few scat- 

 tered ganglion cells are to be found along the course of the dorsal 

 nerve, but in Ncuroncmcrtcs aurantiaca this nerve is very large 

 and is provided with a series of nervous structures, apparently of 

 the nature of ganglia, although such organs have not hitherto been 

 found in any species of nemertean. In my monograph on the 

 Pelagic Nemerteans (Coe, '26) they were referred to as "prob- 

 lematical organs " although their probable nature as ganglia was 

 emphasized (p. 130). 



The number of these organs is upward of a hundred, cor- 

 responding presumably to a primitive metamerism. 



Anteriorly the ganglia are somewhat smaller than the diameter 

 of the fibrous core of the dorsal nerve, but farther back in the 

 body they are several times as large as the nerve and are often 



