12 BULLETIN OF THE 



distinct bounding membrane (mb. pi ph.). This can be called the periph- 

 eral membrane. The four cells in each group are separated one from 

 another by delicate membranes (mb. i cl.), which often show undoubted 

 continuity with the peripheral membrane. These membranes, since they 

 lie between the cone-cells, can be called the intercellular membranes. 

 The distal end of each cell contains coarsely granular protoplasm and a 

 nucleus (Fig. 4, nl. con.). The nuclei usually lie in the external angles 

 of the cells, and do not readily take up coloring matter. The terminal 

 granular protoplasm of the four cells forms a distal cap (Fig. 1, cap.). 

 This cap fills the concavity on the proximal face of the corneal hypo- 

 dermis, and its central distal tip probably passes between the pair of 

 hypodermal cells and touches the cuticula. The spot or cross which is 

 thus probably produced in the centre of each facet has already been 

 described. 



Below the cap of granular protoplasm is the crystalline cone. The 

 firm peripheral membrane of the cap is continued over the cone and 

 proximal part of the cone-cell. The distal end of the cone in cross- 

 section is a square with rounded angles. At this end there is no indi- 

 cation of a division of the cone into four segments corresponding to the 

 four cells. A transverse section midway the length of the cone (Fig. 5) 

 shows no features essentially different from those of the section across 

 the distal end. The proximal end of the cone in cross-section is nearly 

 circular (Fig. 6). On the sides of this end of the cone one often notices 

 small re-entrant angles (Fig. 6, x). The peripheral membrane dips into 

 these. The angles are usually four in number, never more, and occupy 

 positions which indicate the planes of separation between the four cone- 

 cells. In some cases delicate membranes originating from the angles di- 

 vide the substance of the cone into its four constituents (Fig. 6, mb. i cl.). 

 These membranes correspond in position to the intercellular membranes 

 at the distal end of the cone-cells. The substance of the cone is very 

 finely granular. The four constituents of each cone terminate very 

 nearly at one level. In passing in a proximal direction through a series 

 of sections, the substance of the cone is last seen as a thickening which 

 flanks the cell membranes, especially the intercellular membranes. 

 (Compare Figs. 1 and 6.) 



Below the cones the outlines of the four cone-cells are well marked 

 by both peripheral and intercellular membranes (Fig. 7). The inter, 

 cellular membranes are continuous with those seen in the proximal ends 

 of some cones. In this region the cells contain coarsely granular proto- 

 plasm. In passing from the deep ends of the cones to the proximal 



