468 SHAFER 



optic ganglion beneath each area are distinct. The corneal 

 lenses over the greater part of the dorsal eye have been torn 

 from this section. The remaining 2 entire elements, however, 

 show the ommatidia in this dorsal eye to be about two and a 

 half times the length of those in the lateral eye. The lens and 

 the pseudocone of a dorsal ommatidia are continuous. That is, 

 the inner surface of the corneal lens is not noticeably separated 

 from its adjoining cone beneath. This is easily seen in micro- 

 photograph 29 and Fig. 15. The rounded apex of each of the 

 pseudocones is denser than the rest of the cone and stains 

 readily. Cross-sections through this denser apex show the 

 cone to be made of 4 cells and the nucleus of each cell is found 

 in this denser part (Fig. 15, A). In the outer larger part of 

 the cone the cell walls cannot be distinguished. Surrounding 

 the tip of each one are 2 very thin primary iris pigment cells 

 (Fig. 15, A, ci-fi). Outside of these, sheathing the distal part of 

 each cone and extending down between the retinulae are 22 to 

 24 slender secondary pigment cells (Fig. A, sip, and Fig. 29, 

 sip). A retinula in this eye is composed of 7 cells — 6 entirely 

 surrounding the seventh for its entire length. The rhabdomere 

 of each cell is distinct (Fig. 15, C, rb). The distal ends of the 

 retinular cells abut closely against the rounded cone tip and in 

 their extreme proximal ends just above the basement membrane, 

 lie the 7 large retinular nuclei (Fig. 15, A, rn). A definite 

 bundle of nerve fibers leads from the base of each retinula 

 through the basement membrane (Figs. 15, A and 29, nj). 



The number and position of the cells in the ommatidia of the 

 lateral eye of this fly is the same as that just described for the 

 dorsal eye. The corneal lenses of the lateral eye are more 

 distinctly formed and the retinular cells as well as the iris pig- 

 ment cells (primary and secondary) are densely packed with 

 pigment. In the dorsal eye the pigmentation in the iris is very 

 slight and it is absent in the retinular cells of this eye. 



CALLIByETIS HAGENI Etn. 



Several references have already been made by different 

 investigators to the condition of the compound eyes of certain 

 mayflies (Pictet, 1845; Ciaccio, 1880; Carriere, 1893; and 



