66 BULLETIN OF THE 
which lies immediately over it. No trace of a suspensory ligament seems 
to be present, nor have I been able to find a processus falciformis. 
In a single instance, viz. in the eye portions of which are shown in 
Figures 13 and 21, and which has already been spoken of as showing 
in several respects a higher state of development than any other speci- 
men studied, I find close behind the iris, within the cavity of the 
eye, a few strands of tissue containing a few small nuclei, which may 
possibly be regarded as the hyaloid membrane, though I do not feel at 
all certain that this is their nature. In the same specimen a very few 
blood corpuscles are also found close behind the lens within the eye 
chamber. With this single exception I have been unable to find a trace 
of tissue within the chamber. 
The optic nerve, although exceedingly slender, is always present, so 
far as my observations have gone. A very striking fact in connection 
with it is the thick sheath of pigment that surrounds it in its passage 
through the retina (Figs 6, 13, and 15, pig.'’). This sheath invests the 
nerve very closely, no space existing between it and the latter ; however, 
in its course through the retina, a considerable non-pigmented space is 
sometimes seen between its outer surface and the pigment of the ret- 
ina; indeed, in a majority of cases the outer boundary of the sheath 
can be traced entirely through the retinal pigment. 
These facts make me incline to the opinion that this sheath really 
belongs to the nerve, and has arisen by the pigmentation of the outer 
portions of it. The fact that in many cases it continues on without 
interruption through the cellular portion of the retina, nearly to its 
inner surface (Plate II. Figs. 6 and 13), gives considerable confirmation 
to this view. It would seem, however, were this the right interpreta- 
tion, that we should find a rather more gradual disappearance of the 
pigment in passing, on a section, from the main mass of the wall of 
the sheath to the unpigmented portion of the nerve, than we do; but 
the inner surface of the sheath is not quite as sharply defined as its 
outer surface is. 
On account of the position of the eyes, far anterior to the brain, and 
near the anterior extremity of the head, the optic nerves are very long. 
The muscles of the eyeballs (Fig. 8) are also very long and slender, 
and are probably always present, though I have not been able to detect 
them in the sections in all cases; but in eyes dissected out and cleared 
in glycerine or clove oil, or slightly stained in Schneider’s acetic acid 
carmine, I have always found them. Figure 8 is a camera drawing 
from a glycerine preparation, showing all the muscles excepting the 
internal oblique, and also the nerve. 
