814 
ROSS GRANVILLE HARRISON 
mass of tissue a long stout process of hyaline protoplasm, which, 
when first observed, was about 90 ^ in length, and extended out 
from a tapering cell (fig. 7). Examined an hour and a half 
later, this process was found to be only a little (about 17m) longer, 
but the form of the end had changed considerably (fig. 8). It 
could also be seen that there were two separate fibers instead of a 
single one, one partly overlapping the other. Eight hours and a 
half later the specimen was again examined and found to have 
undergone remarkable changes (fig. 9). No less than four fibers 
could then be distinguished diverging from one another in their 
direction of growth, and each with its characteristic branched 
end (npl) continually undergoing change in form. The longest 
fiber (nfz) was about 220^ in length. At this time the prepara- 
tion closely resembled the condition described above in the nor- 
mal embryo (figs. 3 and 4). Another interesting and important 
feature shown by this preparation was the action of the fibrin 
(thr) upon certain of the cells (0^2), and the independence of the pro- 
toplasmic filaments from the fibrin threads. Twelve hours later, 
on the following morning, the change noticed was again very 
striking (fig. 10). Two of the fibers (n/2 and n/3) were branched 
and all had lengthened materially, the longest being about 
480 M in length. The ends of the fibers continued to show the 
same activity as before. Throughout their entire length the fibers 
consist of hyaline protoplasm, with no yolk nor pigment granules 
whatever. Slight varicosities are present in places, and often the 
fibers show a faint fibrillation and sometimes are slightly mottled. 
The thickness of the fibers, 2-3^, in this case is rather unusual. 
Changes in the cells are also important. The number of loose 
cells has increased, and they move along slowly from place to 
place, while changing their shape. Their movement is, however, 
entirely independent of the fibers. The tension of the fibrin 
filaments upon some of the cells is clearly shown. The cell (0^2) 
noticed previously is very much drawn out as compared with its 
condition the day before. Eleven hours later still further elonga- 
tion and branching of the nerve fibers is to be seen (fig. 11), the 
longest now being about 600//. The loose cells are more num.erous 
and some of the fibers are partly obscured by them. The exact 
