464 The Giant Nerve Cells and Fibres of Halla parthenopeia. 
distances down the cord. One or more short branches issue from the giant 
fibre near the angle of decussation, and, as the fibre runs along the dorsal side 
of the nerve cord, branches issue which fork, the twigs pass to the right and 
left, they taper, their sheath disappears, and the protoplasmic axis of each 
twig, now about ly in diameter, is lost to view in the lateral or ventro- 
lateral region of the neuropile, in no case could it be traced into a spinal 
nerve. 
The sheath of the giant cell and giant fibre is not blackened by the action 
of osmic acid, it consists of glia fibrils of various thickness, among which 
glia nuclei and the granular remains of glia protoplasm are present. 
The neurofibrillar network in the giant cell is divisible into a peri-nuclear 
network, situated at the margin of the peri-nuclear zone, and a more extensive,, 
wider meshed, and generally more slender stranded network in the general 
protoplasm. From this network slender primitive fibrils pass into the cone 
of origin of the axone, whence stouter fibrils (0°2 to 0°25 w thick), each due to 
the fusion of several primitive fibrils, pass into the giant fibre. The number 
of fibrille issuing from the cell varies according to the size of the cell: 
6 to 10 issue from the small giant cells, 12 to 30 from the larger ones. The 
bundle of neurofibrille probably does not fill the lumen of the fibre in life 
(fibrille could not be seen in the living or fresh giant fibres), but occupies 
from one-fourth to three-fourths of the internal diameter of the fibre, the 
remaining space being filled with the semi-fluid, finely-granular “ peri-fibrillar 
substance.” Between the fibrils there is a more homogeneous “ inter- 
fibrillar substance.” The fibrille in a giant fibre are usually all of the same 
thickness, but in several fibres there are one to three fibrils thicker than 
the rest. 
The contents of the giant fibre are equivalent, and have a similar structure, 
to the axis cylinder of a medullated nerve, except that in the former there is 
nothing comparable to the Ranvier’s nodes of the latter. 
The anterior giant cells of Aglawrides fulgida are also segmentally arranged, 
there being a couple in each of the first four, five, or six segments. The cells 
seem to have attained their maximum diameter (90) when the worm has 
reached a length of 14cm. In the main features of their structure and of 
the arrangement of their neurofibrillar network the giant cells of Aglawrides 
agree with those of Halla. 
Sharply and deeply stained fibrils penetrate the sheath of many of the 
giant cells of Halla and Aglawrides, enter the cell and apparently join the 
intracellular network. Numerous short fibrils, probably of glial nature, enter 
the peripheral zone of the giant cells of Halla. 
