26 bulletin: museum of comparative zoology. 



[Figure 6 (Plate 1) and compare with it other sagittal sections (Plate 5, 

 Pigs. 44, 46, 48) as well as cross sections (Plate 5, Figs. 45, 49, 50). 

 In Figure 6 (Plate 1) are shown the ventral eye, at the right, in contact 

 with the central cell [cl. c.) at three places, and the optic nerve (n. opt.) 

 leaving the eye as a single bundle of fibres, which results from the 

 union of three divisions lying in the median plane of the whole eye, 

 between the lateral cups. The dorsal division passes through the 

 central cell, between the paired ocelli, from the anterior border of the 

 cell, and is shown in greater extent in Plate 5, Figure 44. The ventral 

 and posterior of the three median divisions of the optic nerve (in Plate 

 1, Fig. 6) leaves the ventral eye at the posterior end, between the basal 

 plate and the bounding membrane of the eye (compare Plate 5, Fig. 46). 

 As regards the middle bundle, the way in which it leaves the ventral 

 eye is shown in the sagittal sections in Figures 6 (Plate 1), and 44, 46, 

 48 (Plate 5), with which the cross section shown in Figure 50 (Plate 5) 

 should be compared. Figures 6 and 50 show particularly well that the 

 nerves which leave the central portion of the ventral eye pass through 

 an opening in the basal plate. Frontal sections of the eyes show 

 that there are lateral, as well as median, divisions of the optic nerve 

 (Plate 1, Fig. 2). 



In the cross-sections represented in Figures 45, 47, and 49, which are 

 three of a series of 8 sections, and are successive (Fig. 47 being posterior 

 and Fig. 49 anterior), the same conditions are encountered. In Figure 

 45 (Plate 5) are shown 28 axis cylinders {fhr.) in approximate cross 

 section. There are five in each lateral division, two leaving the ventral 

 eye, and sixteen others are in a median group though their departure 

 from the retinal cells is not shown in the section. In the section an- 

 terior to this (Plate 5, Fig. 49) there are thirteen fibres in the central 

 cell: of the five lateral ones shown in Figure 45 the distribution of 

 those which are more dorsal cannot be followed, though that of the 

 remaining four is shown in relation to the left lateral ocellus (or. s.). 

 Three fibres leave the lateral eye and one (on the same side) leaves the 

 ventral eye. The cell of the ventral eye shown on the right is the 

 left cell of the second pair from the posterior end of the eye (cf. Plate 1, 

 Fig. 8). It will be noted that the fibres in this section, which are 

 distributed to the ventral eye, pass lateral to (I'ight and left of) the 

 basal plate instead of through it. 



In the next section anterior, (Fig. 50) six fibres are shown which are 

 still in the pigment cell, while two others diverge toward the lateral 

 eyes, and one more is barely distinguishable in the ventral portion of 

 each of the lateral eyes. In the ventral eve may be seen the central 



