Langdon, Sense-organs of Nereis virens. 49 



each process arches toward the central tube and its refractive 

 body appears to be joined to a thick band which is wound spir- 

 ally around the tube. The protoplasm of these peripheral pro- 

 cesses as seen in living material, appears to be made up of 

 transparent semi-liquid drops contained in the meshes of a very 

 coarse, highly refractive network. In a few of my methylene 

 blue preparations, there appears to be a nucleus lying 

 close against one side of the enlarged end of a peripheral pro- 

 cess. In material killed by alcohol or Miiller's fluid, this ap- 

 pearance is never seen. The highest powers of the microscope 

 and the most careful focusing never reveal any structure in a 

 living peripheral process except the protoplasm previously 

 described and the apical refractive body. As the nuclei in the 

 cell bodies are clearly seen in living material, I believe, if one 

 existed in the enlarged part of a peripheral process, it too 

 could be seen. Moreover, in methylene blue preparations ex- 

 amined when the tissues are living, there is no trace whatever 

 of the apparent nucleus seen in the permanent methylene blue 

 preparations. In the latter, the spiral organs are poorly pre- 

 served. Each peripheral process is much vacuolated and its 

 protoplasm is consequently reduced to mere threads or films 

 which are forced against the wall of the process. The apparent 

 nucleus seen in these preparations seems to me to be merely a 

 thicker place of one of these threads. 



The refractive bodies are clear, lens-like structures which 

 take the stain but faintly, if at all. Each, when viewed from 

 above, is generally rounded at the end away from the central 

 tube and tapers from this end toward a slender rod-like part 

 which rests upon the outer surface of the spiral band previous- 

 ly mentioned (PI. II, Fig. 43). These rod-like parts give this 

 band an appearance resembling the rim of a cog-wheel. (PI. 

 II, Fig. 49 g). The refractive bodies belonging to the periph- 

 eral processes, which pass to the deep end of the central tube 

 seem to rest, when seen in living material, directly upon the 

 tube itself. Sections, however, show that the spiral band is 

 also present here, making its last turn around the base of the 

 tube. When viewed from the side, it is seen that each refrac- 



