DIVIDED EYES OF CERTAIN INSECTS 463 



in a thin band, /, which marks its lower boundary along the dis- 

 tal ends of the retinular-like bodies. 



4. A black pigment similar to that along the retinula sur- 

 rounds the retinular-like bodies, and ends at the proximal ends 

 of these bodies in a narrow densely black band of pigment, gp 

 (Figs. 3 and 4, A). This in Sicyonia sculpa, has been named the 

 pigment or tapetum sheath of the optic ganglion by Exner, 1891. 



The same description of pigment holds for the large omma- 

 tidial part of the eye except that the iris pigment and retinular 

 pigment in this case are brownish yellow and everywhere in 

 this part of the eye the pigment is very much less dense than 

 in the small ommatidial region. 



ANAX JUNIUS Drury. 



The facets of the compound eyes of the male of Anax Junius 

 are not all of the same size. Facets may be found that differ 

 as much in size as those of the different areas on the eye of 

 Sympetriim, but no line divides the eye of Anax into 2 regions. 

 In this case the larger facets are found on the upper and inner 

 surfaces of the eyes, and the smaller facets on the outer lower 

 margins. The 2 sizes grade into each other. It was not until sec- 

 tions were made of the eye that this condition was noticed. Fig. 

 12 was made from a cross-section of the head of a male Anax, 

 cut in a plane passing through the ocellus and perpendicular to 

 the facet area of the compound eye. The figure shows clearly 

 this gradation of the large facets on the upper inner part of the 

 eye into the smaller ones at the outer margin. As is shown also, 

 along with this gradation in the size of facets, the elements of 

 the ommatidia pass through a like gradation in size and length. 

 Moreover, a similar but reverse condition holds for the pigmen- 

 tation in this eye. Around the smaller shorter elements at the 

 outer margin of the eye the pigment is densest and occupies the 

 whole length of the retinula?. Passing toward the inner part of 

 the eye, the pigment becomes less and less dense around the 

 proximal ends of the retinula; until in the region of the largest 

 ommatidia almost no pigment is present except the iris pigment. 

 Other than this difference in size and pigmentation, the large 

 and small ommatidia are very similar as may be seen in Figs. 



