Langdon, Sense-organs of Nereis virens. 27 



into spherical drops." Allen evidently considers that the entire 

 nerve-fiber takes part in the formation of these varicosities ; 

 both Dogiel (93) and Ruber ('97) have called attention to the 

 fact that in vertebrate nerve-fibers it is the neuroplasm alone 

 which swells under the influence of post-mortem changes and 

 forms varicosities on the more resistant axial strand. In my 

 own work with Nereis, I have been able to see that in the nerve- 

 fibers it is usually the neuroplasm alone that forms these vari- 

 cosities. Since the granular axial strand is lacking in the sen- 

 sory hairs it must be that here also it is the neuroplasm that 

 swells when death allows surface tension to act. 



C. Course of the Central Processes to the Central Nervous 

 System. 



As before stated, the central processes of the diffuse sense- 

 organs found in the body epidermis, including those in the base 

 of the cephalic cirri and palps, were but rarely stained for any 

 distance. It has, therefore, been impossible in my methylene 

 blue preparations to trace these central processes directly into 

 the central nervous system. In a few cases these processes 

 could be seen to enter the nerves in the base of the epidermis. 

 In the prostomium these epidermal nerves pass to the brain ; in 

 the rest of the body to the ventral nerve-cord in the metamere 

 in which the epidermal nerve in question is situated. 



In the various appendages, the central processes were so 

 well stained by the methylene blue that they could be traced 

 directly into special ganglia or into the brain itself 



The nerves from the anterior or internal pair of cirri pass 

 into a small ganglion which is situated on the circum-oesopha- 

 geal commissure just ventrad to the point at which this commis- 

 sure divides into its larger dorsal and ventral roots. The nerves 

 from the posterior or external cirri pass to a second ganglion 

 slightly latero-ventrad of the first. From this ganglion a 

 separate nerve passes to the anterior end of the sub-cesophageal 



