— 39 — 



1-st nnd 6-th cells is placed an extremely narrow 7-th retinal 

 cell. The plane of symmetry passes between the 3-rd and 4-th 

 cells, dividing the 7-th cell on a half. I did not sncceed in 

 discovering any traces of the 8-th cell in the retinula of 

 Diopsidae. Bnt it is possible that remnants of the 8-th cell 

 are to be found in the distal part of the retinula, as it seems 

 to me that in this place the regularity of arrangement of the 

 cells is to a certain degree interrupted, on account of the 

 7-th and 1-st rhabdomere converging together. In general, the 

 arrangement of the rhabdomeres (fig. C) is such, that the 7-th 

 rhabdomere is situated at the point of crossing of two right 

 lines, of which one joins the l-st with the 5-th rhabdomere, 

 and the other — the 2-nd and 6-th. This is a general rule, which 

 seems to be supported by Dietrich's drawings as well 

 (fig. B). 



I must also, in accordance with Dietrich, state that the 

 eye is composed of two parts, each representing the mirror 

 reflection of the other (see what was said above with regard 

 to fig. 13). 



The Pigment. 



The pigment surrounds the ommatidia of Diopsidae from 

 all sides like a sheath; it does not extend into the optic ganglia, 

 on the other side of the basilar membrane. Both in insects 

 generally, and in Diopsidae there are to be distinguished „the 

 pigment of the iris", and „the pigment of the retina". The 

 pigmentation of the iris is due to the chief and accessory 

 pigment cells. To each ommatidium belong two chief pigment 

 cells which embrace the pseudocone and form a sort of thick 

 membrane around it (cp. fig. 9 and 11, P,). Ji\ fig. 11 the sec- 

 tion passed through the ommatidia somewhat obliquely, on 

 account of which the pigment cells are seen on different 

 heights here: on the left they are nearer to the facef , on the 

 right— nearer to the cells of the crystalline cone. At the edge 

 of the facet the chief pigment cells taken together have a 

 hexagox d shape, but they become rounder in the proximal 

 direction, and in the region of the cells of the crystalline 

 cone they are quite round. It is here that they attain their 

 greatest thickness, and further proximally they terminate. 

 The nuclei of the chief pigment cells (n. P^) are situated in 

 the middle of the height of the pseudocone. 



