No. 1.] EVES OF ARTHROPODS. 147 
cess in detail. In Fig. 62 is shown. one of these cells just as it 
has reached the inner surface of the eye. It arose from one 
of the large nuclei found among the closely packed retinal 
ones, from which they are distinguished by their large size and 
coarsely granular contents. As these nuclei descend into 
the clear space at the inner surface of the eye they in- 
crease rapidly in size, and a great mass of finely granular 
protoplasm collects around them so that they become very 
conspicuous objects in sections of the eye at this period. 
The cells are distinctly tripolar. One of the prolongations is 
always directed outwards. Its base, which is broad and filled 
with protoplasm like that in the cell, is continuous with a tube- 
like prolongation. Owing to its wavy course and to its clear 
contents, which cause it to stand out clearly against the dark 
protoplasm of the retinal cells, it is not difficult to follow this 
tube a considerable distance into the tissues of the eye, where it 
is finally reduced to a thin refractive fibre that disappears be- 
tween the retinal cells. The two inner prolongations do not 
become visible until the cell has reached the innermost part of 
the eye. They are less conspicuous than the one just described, 
for they are smaller, and the dark protoplasm extends into them 
a short distance only. They usually arise from opposite sides of 
the inner surface of the cell and extend in opposite directions at 
right angles to the outer fibre. But there is considerable irregu- 
larity in the position of the fibres. In some cases it looks as 
though the nucleus moved inward faster than the rest of the cell, 
leaving the inner fibres behind. It frequently happens that the 
latter are directed at right angles to the section plane; the cell 
then assumes a shape like that in Fig. 82. One often sees a 
cluster of four or five enormous cells midway between the eye 
and the optic ganglion (Fig. 63, z. g.c.). Most of these cells are 
converted by rapid division into small pear-shaped ones which 
gradually move inwards along the optic nerve, forcing a way for 
themselves between the fibres, until they are finally lost among 
the similar cells of the optic ganglion. But one of the cells 
retains its great size. When it reaches the optic ganglion, it is 
pushed to one side, out of the nerve root; its inner end is swung 
outward toward the periphery of the ganglion and the outer 
prolongation, which is now more conspicuous than ever, is bent 
almost double. Between the bend and the cell itself, the pro- 
