208 



HEMENWA Y. 



[VOL. I. 



Surrounding each ommatidium are elongated pigment cells, 

 extending the entire length of the ommatidium (Fig. i B). At 

 both distal and proximal ends these pigment cells become 

 expanded, the pigment granules collecting in the expanded 

 portions. At the proximal end this gives the pigmented ap- 

 pearance of the basal membrane, spoken of by Grenacher. 



There are sixteen to eighteen of these pigment cells belong- 

 ing to an individual ommatidium. The nuclei are visible with- 

 out reagents, but are more clearly shown by methyl green. 



''V v ^' // 



i:p7 , ' / 



A- 



Iff -. -.:-'.;--,... -- . . ; 



* 



FIG. i. 



They are found at the same level as the nuclei of the middle 

 tier of cells (Fig. i A), Each ommatidium consists of a clear, 

 crystalline body, surrounded by three tiers of cells ; the outer 

 consisting of twelve (/i), the middle of ten to twelve (/ 2 ), and 

 the inner tier of three to four cells, respectively (/ 3 ). 



The cells of the outer tier are large and flat and deeply 

 pigmented at the proximal ends, the pigment granules being 

 extremely large and round. The nuclei did not show in a 

 macerated specimen, owing to the pigment. 



The middle tier of cells are called by Grenacher the "outer 

 retinular cells." They are longer and more narrow than the 



