esterly: eucalanus. Zb 



section is unfavorable, it is practically impossible to trace the indi- 

 vidual nerves. 



As previously stated, the optic nerve leaves the central (or pigment) 

 cell of the eye at its posterior border, the axis cylinders having 

 passed through that cell in their course from the visual cells of the 

 eye. The fibres can enter the pigment cell only at the points where 

 the optic cups are in contact with the central cell. Figure 2 (Plate 1) 

 shows that the lateral optic vesicles are separated from the tapetal 

 laver of the pigment cell everywhere (at the level of the section) except 

 at the anterior angle of the anterior basal plate and at the posterior 

 angle of the posterior plate, and that in these places the tapetum is. 

 interrupted. In cross sections (Plate 5, Figs. 49, 50), it can be seen 

 that the lateral eyes (Plate 5, Fig. 49) are in contact with the central 

 cell (cl. c) at the dorsal and outer ventral margins of the latter; and in 

 serial cross sections it is shown that the eyes touch the central cell 

 along its entire dorsal and ventral margins, for in no section of such 

 series are these connections broken. But it should be said that where- 

 ever the lateral eyes and central cell come in contact, the surrounding 

 capsular membrane of the eye vesicle is present. I believe that the 

 spaces separating the eyes from the central cell (Plate 1, Fig. 2; Plate 4, 

 Figs. 49, 50) are not artifacts due to shrinking, because they occur 

 in every preparation, no matter what the treatment may have been, 

 and in all preparations the conditions are precisely as described. 

 Again, it seems reasonable to maintain that, if the spaces were due to 

 shrinkage, there would be evidence to this effect in wrinkling or 

 irregularities of outline, but this is not the case. 



In the ventral eye, the relations of the central cell and optic cup are 

 similar to those described for the lateral eyes. P'igures 6 (Plate 1), 

 44 and 48 (Plate 5) show that the two are in contact at the anterior 

 and posterior margins of the eye and also at a point midway between 

 the two. As in the paired eyes, the tapetum (tap.) is interrupted where 

 the eye touches the pigment cell (cl. c) . These anterior and posterior 

 regions of contact also mark the anterior and posterior limits of the 

 basal plate of the eye, but the other place of contact is through an 

 opening in the basal plate, the plate being continuous lateral to the 

 region of contact, as it is anterior and posterior to it. (Compare 

 Plate 1, Fig. 0, and Plate 5, Figs. 49 and 50.) The ventral component 

 and the pigment cell (Plate 5, Fig. 49) are also in contact lateral to 

 the basal plate (la. ha.) of the ocellus and nerves leave the retinal 

 cells at these points. 



As a basis for describing the nerve supply of the eye, we may take 



