No. 4-] THE EYE OF SCUTIGERA FORCEPS. 209 



cells of the outer tier, reddish in color, lacking the black pig- 

 ment of the outer tier. 



(Fig. i) D tz shows two of these cells with the nuclei at the 

 extreme distal portion. At the proximal end each cell is pro- 

 longed into an extremely fine "tail," which runs down between 

 the cells of the inner tier and is continued through the basal 

 membrane as a nerve fiber. 



The cells of the inner tier have their proximal ends bordering 

 upon the basal membrane. From the proximal ends fine 

 processes continue through the basal membrane to form the 

 nerve fibers. The cells are much broader than those of the 

 middle tier. 



Cross-sections through the different levels show the crystal- 

 line body occupying the central axis of the ommatidium, sur- 

 rounded by a clear zone or rhabdom forming the inner parts 

 of the cells of the ommatidium (Fig. 2 B, r). The clear zone 

 is formed of the structures called by Grenacher the rhabdoms 

 - a secretion product of the retinular cells. In macerated 

 specimens these rhabdoms were visible upon the inner surface 

 of each cell of the two proximal tiers (Fig. i C) and could be 

 made to separate from the cell by tapping. The "tail," or 

 nerve, is on the opposite side of the cell from the secreted por- 

 tion. The secretions from the inner tier are thicker than from 

 the middle tier, and in cross-sections appear roughly triangular 

 in shape (Fig. 2 F}. There were no nerve fibers observed for 

 the outer tier, and it differs in this respect from the two inner 

 tiers. In certain cases, after tapping, the outer cells unfolded, 

 as it were, and spread out into a band. The distal ends are 

 rounded, while the proximal ends are drawn down into a point 

 which extends between the distal ends of the middle tier. 

 Thus the nuclei of the middle tier are found between these 

 points of the outer tier (Fig. I A). 



The series of cross-sections (Fig. 2 AF) are taken at the 

 levels of the different nuclei. 



I. The first section beneath the cornea is shown in Fig. 2 A. 

 It represents the extreme distal portion of the ommatidia. 

 A few large nuclei are found at this level, situated between the 

 individual ommatidia. 



