No. I.] EYES OF ARTHROPODS. 109 
A careful study of sections and isolated cells shows that the 
pigment is distributed in granules along the nerve fibres that 
cling to the walls of the retinophore. Toward the inner ends 
of the latter, the course of the external nerve fibres is often 
distinctly marked out by the pigment granules deposited upon 
them. (Pl. X.; Fig, 58). "At the jouter ends voit the cells, the 
external nerves are straight and close together. Where 
there is little pigment, one can see that the granules are ar- 
ranged in rows around each of these nerve fibres (Figs. 56 and 
57). Usually, however, the pigment forms a continuous and 
uniform envelop around the outer ends of the cells, where it 
terminates abruptly, while the nerve fibres are continued on- 
wards over the outer surface of the rods. If there is any 
pigment at all inside the cells, it must be deposited in a very 
thin layer in, or just beneath, the cell wall. 
Just below the inner ends of the rods, cross sections show a 
mosaic of deeply pigmented, hexagonal blocks, from which we- 
might conclude that here pigment was lodged inside the cell 
walls. But isolated cells show that pigment is deposited between 
the flattened and diverging ends of the two cells composing each 
retinophora ; consequently we may not conclude from these solid 
blocks that the pigment is necessarily inside the retinophore. 
Again, when the larva had died a so-called natural death, or 
perhaps owing to other conditions of which I was ignorant, the 
pigment dissolved, staining the retinal cells dark brown through- 
out. Of course, in cross sections of such material, pigment 
would appear to be deposited inside the cell wall. 
There is proof in the optic nerves, that some of the pigment, 
at least, is an intercellular product. or in sections and in 
loosened or isolated fibres, it is evident that the pigment gran- 
ules are scattered about between the fibres, and not in them or 
in any distinct cells. 
In the peripheral cells of the retina, and in those which con- 
stitute the outer wall of the optic vesicle, the pigment is 
coarser and less regularly arranged, resembling in general ap- 
pearance that found in the iris. This fact enhances the decep- 
tive appearance, already mentioned, that might lead one to think 
the retina was directly continuous with the iris and surround- 
ing ectoderm. In the iris, the pigment is undoubtedly depos- 
ited inside the cell walls. 
