40 Journal of Comparative Neurology, 



often found an appearance of rounded glistening bodies which, it seems 

 me, might be parts of the surface of an enclosed ganglion cell. 



Hamaker ('98) decided that in N. virens each nerve fiber of his 

 "set e" is "apparently centripetal, since no cell was found connected 

 with it" and is equivalent to the sensory fibers of Lumbricus. These 

 fibers enter the ventral nerve-cord through the fourth nerve, divide into 

 an anterior and a posterior branch, the anterior branch divides again, 

 and all three end in "fibrillations." Moreover some of the branches 

 "lie side by side and are connected with one another by several ladder- 

 like anastomoses." It seems to me unlikely that the sensory fibers 

 should enter the ventral nerve-cord only by one of the five pairs of 

 nerves found in each metamere of Nereis — unlikely both from the num- 

 ber and position of these organs and from the fact that in Lumbricus 

 their central processes are found in all of the nerves in a metamere. 



From his illustrations, I judge that his fibrillations are not the 

 same as the appearances which I have called "apparent pericellular 

 nerve-baskets " — appearances which are often found in the very gang- 

 lionic center to which the central fibers of the diffuse sense-organ can 

 be directly traced and in which, as far as I have been able to deter- 

 mine, these same fibers are the only onea in my preparations that are 

 stained by the blue. The mere fact that a given fiber is centripetal 

 does not seem to me to be sufficient evidence that it is the central pro- 

 cess from a cell in any epidermal sensory system. From the evidence 

 now at hand it appears to me unlikely that the centripetal fibers de- 

 scribed by Hamaker can be the central processes from the nerve-cells 

 of the diffuse sense-organs. It will, however, need a careful tracing, 

 on the one hand, of an individual centripetal fiber of the fourth nerve 

 to its peripheral end, and on the other hand, of an individual central 

 process from a single cell in a diffuse sense-organ to its central end in 

 order to definitely settle this question. 



As far as the final terminations of these central processes are con- 

 cerned, my own observations make it seem possible to me that these 

 will be found to be pericellular nerve-baskets rather than end-bushes 

 or fibrillations. 



The only previous accounts of pericellular nerve-baskets in the 

 worms are those given by Retzius {'92c) and Simon ('96) for the leech- 

 es. Retzius figures and briefly mentions what appear to be undoubted 

 nerve-baskets around ganglion cells in the brain of Hirudo and the 

 ventral nerve-chain of Aulastomum. None of the appearances seen by 

 me in Nereis have as closely resembled the nerve-baskets of vertebrates 

 as those figured by Retzius. Some of the pericellular baskets figured 



