18 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
character of the individual bodies in the masses which frequently 
occur. But other more or less irregular shapes may be seen, and 
are shown in the most of my figures. But here, as in the case of the 
bands or ribbons, I believe that the identity of the rod-like bodies is 
either lost by dense staining or not revealed because of too light stain- 
ing. 
The adequate illustration of the interior bodies in a cell is impossible. 
In all cases where they are shown they have been drawn as accurately 
as possible, but in no instance has any attempt been made to show all 
the bodies that are present. More attention has been paid to giving 
an accurate idea of the general appearance of a preparation, than to 
showing every detail in regard to the interior bodies. 
The interior bodies in themselves appear to be homogeneous and 
structureless; no preparations that I have show them to be more than 
that. 
But the shape and structure of the interior bodies — the questions 
as to whether the units are rod-like, or band-shaped, or both — are 
subordinate in importance to the arrangement of the bodies in the 
retinal cells, and the relation of this arrangement both to the direction 
of the nerve fibres in the retinal cells, and to the axes of the optic cups. 
In order to, put this matter as clearly as possible, it will be necessary to 
describe the position of the optic cups, both with reference to the body 
of the animal and to each other. 
The median, longitudinal axis of the ventral eye, as well as the optic 
nerve, lies exactly in the sagittal plane of the body, and the transverse 
axes are perpendicular to that plane. 
The long axes of all the cells of the median ocellus of the eye are 
perpendicular to the median plane of the body (Plate 1, Fig. 8). It 
is difficult to describe the axes of the central cell in this part of the 
eye, for the cell is quadrangular as seen in frontal section (Plate 1, 
Fig. 8), the sides being of about equal length. But in Figure 8 the 
longer axis is parallel to the long axes of the remaining cells. The 
dorso-ventral dimension of the cells in the unpaired eye is approxi- 
mately one-half that of their longest axis. 
The chief axis of each lateral cup is a line perpendicular to the me- 
dian side of the cup at its middle point. As is shown in Figures 7 and 
9 (Plate 1), such a line makes an angle of 45° with the sagittal plane, 
and with the dorso-ventral axis of the ventral eye, all three axes lying 
in the same transverse plane. In Figure 7 the cell which lies at the 
middle of the inner wall of the lateral eyes is the inner cell of the 
median group of three already described, ane its long axis almost 
