126 PATTEM. [Vot. II. 
sheets of vertical fibres, they form amass of the finest, interwoven 
fibrille, that presents the same appearance as the medullary sub- 
stance in the optic gangla. It cannot be that this enigmatical 
mass of nerve fibres is nothing but a flake of coagulated serum. 
The latter is frequently present and is especially abundant after 
some modes of treatment, filling all the cavities of the head 
with a finely granular substance. At other times it is altogether 
absent, or at any rate the cavities appear quite empty. But 
under both these conditions, this mass of nerve fibres, unen- 
closed by any membrane and devoid of nuclei, maintains such a 
constant shape and uniform appearance as to preclude all thought 
of its being a product of coagulation. It may be remarked, also, 
that the coarse pigment granules, so abundant about this fibrous 
mass, are completely dissolved by acids, and consequently leave 
no granular residue that might be mistaken for nerve fibrille. 
We have already pointed out that in the iris the pigment is also 
completely dissolved by these reagents. 
One occasionally finds, among the fragments of cells isolated 
by maceration, what appear to be large flakes of pigment with 
parallel striations. They are fragments of the sheets of ver- 
tical nerve fibres covered with pigment, the fibres being united 
with one another by the innumerable fibrille that arise from 
them. 
Between the outer ends of the vertical nerve fibres is an oval 
space devoid of pigment, quite constant in shape and size (Figs. 
go and of, Pl. XIII). I have no suggestion to make concerning 
its significance. 
The vertical fibres, and the pigment surrounding them, do not 
extend beyond the outer edges of the large rods. 
The Rods in eyes I. and III. develop in the same way as those 
of eyes V. and VI.; and although their arrangement in the fully 
developed eye differs in some important and interesting particu- 
lars from that in the last-mentioned eyes, their general struct- 
ure is the same in both cases. ¢ 
The horizontal rods are arranged with great precision and 
regularity edge to edge in vertical rows. The broad sides of 
two rods belonging to adjacent retinophore lie so close together 
as to look like one rod with a faint vertical line in the middle. 
The rods belonging to the same retinophore are separated 
by a clear space, a little smaller in diameter than that of the 
