110 PAITEN. [Vot. II. 
THE RETINAL Rops AND NERVE EnpiNGs. — Since the retin- 
ophore are closely packed in the retina and the rods are on the 
periphery of their outer ends, it follows chat the rods of two 
neighboring retinophore are placed side by side so that they often 
appear like one vod, while those of the same retinophore are sepa- 
rated by a wide space. 
In eye V. (Fig. 54a) there is a beautiful mosaic of brilliantly 
refractive rods which form regular hexagonal figures, in the 
centre of which are the axial nerve fibres, and on opposite sides, 
the two rods belonging to the same retinophora. On two of 
the sides no rods are developed; only a thin membrane sep- 
arates the adjoining hexagonal spaces at those points. Hence 
under a low magnifying power, the rods appear to be arranged 
in nearly parallel, zigzag lines. 
It is impossible to see the axial nerves in the isolated retin- 
ophore, owing to the twisting of their component cells. But 
they are visible in cross sections as a single bundle in each 
retinophora. In the clear space between the two rods, the 
nerve breaks up into three or four fibres arranged in a plane 
parallel with the sides of the rods. In one of the spaces in Fig. 
54a, they are at right angles to the normal position. Minute 
cross fibrillae arise from these axial fibres, which probably pene- 
trate the rods and unite with the external nerves. The cross 
fibrillaze constitute a vetzzzdzum similar to that of Pecten. Inthe 
latter, each pair of rods has completely fused to form a hollow 
cylinder containing a single axial nerve, from which arise radiat- 
ing cross fibrillz. In Acilius, the two rods are separate and 
flat, and the axial nerve is broken into smaller fibres placed in a 
row, so that a perfect radial arrangement of the fibrillze is impos- 
sible. 
The clear space between the rods is apparently filled with a 
non-refractive fluid in which the retinidial fibrillz are suspended. 
It often contains fine granules, produced, I believe, by the coagu- 
lation or varicosities of the fibrille. The space is exactly like 
that in the centre of the rods of Pecten, and is undoubtedly an 
entercellular one. 
That the cross fibrillae penetrate the rods, I do not doubt, for 
they are marked with cross striae continuous with the fibrillze in 
the clear space. Neither do I see any reason to doubt that the 
fibrillz in the clear space, as well as those in the rods, are 
