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 gi\ing 

 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 0])tic 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 ]:)lane. 



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 eve, all three axes Iving: 

 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, anc' its long axis almost 



