110 bulletin: museum of comparative zoology. 



demonstrated the commou occurrence, in the cells of the brain and 

 ventral ganglia, of such cytoplasmic structures as are represented in 

 Figures 1-9. 



Figures 1, 2, and 3 represent cells from the suboesophageal ganglion 

 of a normal worm, — that is, one that had not undergone regeneration. 

 These cells are from a preparation which was fixed in strouo- Flem- 

 miug's fluid for forty-eight hours and stained in iron-haematoxyliu. 

 The cells are typical unipolar nerve cells, lying in the ventral ante- 

 rior region of the ganglion, with their processes extending dorsally. 

 Figure 4 represents a cell from the dorsal posterior border of the brain 

 of the same animal. 



a. The Nuclei. 



The nucleus of the nerve cell has a characteristic appearance. In osmic 

 acid preparations it is nearly always spherical, or departs only slightly 

 from that form, as in Figures 2 and 4. In siablimate preparations, how- 

 ever, there are often irregularities in form, as seen in Figure 5. Fi'om 

 a general comparison of my osmic-acid preparations with those fixed in 

 sublimate, I am inclined to believe that the nuclei often suffer distortion 

 in sublimate, and that the spherical form represents a more faithful 

 fixation. The excentric nuclei are never flattened nor invaginated, ex- 

 cept in a few cases in which I have observed that one side of a nucleus 

 was indented in such a way as to suggest mechanical distortion due to 

 fixation. So fluid are the contents of the nuclei that it is not strange 

 that such distortions should sometimes occur. These indentations, 

 which are probably artificial, had no regularity in form or in position. 



The nuclei must contain a very large proportion of fluid material 

 which is not coagulated by the fixing agent. In both stained and 

 unstained preparations the nuclei are much clearer than tlie surrounding 

 cytoplasm. They contain a very small amount of matter that takes 

 stain. 



With very rare exceptions, there is but one nucleolus. It is always 

 excentric, often very near the nuclear membrane, and generally departs 

 little from the spherical form. In osmic-acid preparations the nucle- 

 olus is always sharply outlined and never exhibits anything but a 

 perfectly homogeneous structure. It takes a quality of stain different 

 from that of the chromatin, being somewhat brownish instead of dark 

 blue or black. This is doubtless due to the fact that it does not take 

 or hold the stain as strongly as the chromatin, the brown color being 

 due to the osmic acid. 



