OUTGROWTH OF THE NERVE FIBER 
809 
seat in the hyaline ectoplasm fouDd at the angles and sometimes 
at the borders of the cells. The movement cannot be observed 
clearly in the larger masses of cells on account of their opacity, 
but it may be seen very clearly in those cells which leave the main 
masses and wander off by themselves. These cells are irregular 
in shape, varying from unipolar to multipolar form and having 
a varying amount of ectoplasm at their angles (figs. 23 and 27). 
The movement is amoeboid in character and results either in a 
change in shape of the cells or in their movement as a whole (text 
fig. 2). Such cells are found usuallj^ in greatest numbers in prep- 
arations of the medullary cord, and it is here that they are most 
active, though cells from the mesoderm are often quite similar. 
However, it is only the protoplasm of cells from the medullary 
cord and from the cranial ganglia (branchial ectoderm) , that gives 
rise by its movement to long fibers. Cells of the epidermis show 
their power of movement in somewhat different form. As has 
frequently been observed, the general tendency of isolated bits of 
epidermis is to round off into small vesicles, which, when left in 
water, may move about for days by means of their cilia. Within 
the lymph the same thing frequently takes place, although there 
is apparently greater resistance to the process of rolling up, and the 
cells may often remain together in the form of extensive sheets. 
Along the free border of these sheets of cells there often appears 
a fringe of hyaline protoplasm, which undergoes continuous amoe- 
boid changes (figs. 13 and 14p?./r.) In one case of this kind it was 
observed that the sheet of cells gradually spread out toward the 
side on which this fringe was placed. Since the work of Peters 
('85-'89) it has been generally admitted that wound healing in the 
epidermis is primarily due to the movement, in pait amoeboid, 
of the epithelial cells, so that it seems quite possible that in this 
fringe of hyaline protoplasm above described, we have one part of 
the mechanism by which the movement of cells in wound healing 
is brought about. The most inert of all the tissues is the endo- 
derm, which will remain for days in the lymph, practically un- 
changed, gorged with yolk and devoid of hyaline ectoplasm. The 
notochord is also very inactive, although large pieces of this 
structure may show after a time the early stages of normal differ- 
