192 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
semi-fluid, homogeneous substance, which is the first to take up the 
methylen-blue stain. It has been called by Bethe (98) the “ peri- 
fibrillar substance.” The accumulation of this fluid into drops gives 
the characteristic beaded appearance of methylen-blue preparations. 
A distinct nucleated myelin sheath surrounds both the fibre and the 
peripheral ganglion cells of Pulemonetes. This sheath, which stains 
intensely black in Vom Rath’s platino-osmic fixative, can be traced 
some distance beyond the peripheral ganglion cells toward the sensory 
hairs, and also centrally into the brain, where it ceases only when 
the fibres enter the neuropil substance. Figure 16 (Plate 4) shows 
a ganglion cell and its peripheral process surrounded by the sheath. 
Elongated, flattened nuclei occur at intervals along the walls of the 
sheath, curved around it and the enclosed fibre; certain of these 
sheath nuclei can be seen in Figure 4 (nl. tu.) between the ganglionic 
cells and the brain, though the myelin sheaths are not stained in this 
hematoxylin preparation. Quite frequently one of them may occur 
in close proximity to a ganglion cell. Thus are produced (Plate 4, 
Fig. 17) appearances which might be mistaken for a ganglion cell with 
two nuclei. Careful study, however, shows that one nucleus (l.) lies 
within the cell, the other (nl. tu.) without, but abutting on the 
ganglion cell so closely as to sometimes change its form. In every 
instance of this kind one of the nuclei, owing to its irregular outline, 
its smaller size, and the curved form which it takes in adaptation to 
the surface of the cell, could be identified as belonging to the sheath 
rather than to the nerve cell. 
The peripheral ganglion cells are much elongated and are of the 
typical bipolar form (Plate 4, Fig. 18). They measure from 10 to 
14, in diameter; their nuclei are relatively large, measuring from 
7 to 9 in diameter, and are usually ovate in outline, their length in 
some cases being twice as great as their diameter. One large spherical 
nucleolus ig usually present in the chromatic network, though some- 
times two or more are found. No definite structure can be recognized 
in the cytoplasm of the cell, nor any traces of fibrillee; this, however, 
is not strange, as the cell usually stains so intensely that it would not 
be reasonable to expect to make out its finer structure. In methylen- 
blue preparations a narrow zone about the nucleus stains only faintly, 
the coloration becoming more intense as the periphery of the cell is 
approached ; so here, as Bethe also found in the nerve cells of Carcinas, 
the chromatin granules are more numerous at the periphery of the cell 
cytoplasm, and nearly wanting around the nucleus. 
