PLATE XXVI. 



Fig. 17. A. Two ommatidia from the lateral pigmented eye of adult male C. 

 hageni Etn. One element is represented as depigmented, X 



385. 

 B. Cross-section of retinula of A. 

 Fig. 18. A. Two ommatidia of a turban eye of a male subimago of C. hageni 

 Etn. 

 B. Cross-section of retinula of A. 

 Fig. 19. Two ommatidia from the turban eye of a male subimago of C. cali- 

 fornica Banks. An old subimago just before adult was ready to 

 issue, X38.S- 

 Fig. 20. Two ommatidia from the turban eye of male subimago of a mayfly 

 of unknown species showing chief pigment cells. Adult of this 

 species was not reared. 

 Figs. 21 to 22. Eye of nymph of C. hageni Etn. 



Fig. 21. A. A small part of the earliest developmental stage of the turban 

 eye of C. hageni observed. 

 B. Entire eye of a young male nymph at a little later stage of develop- 

 ment than A, i. e., nymph 5 mm. long, X 120. 

 Fig. 22. Entire eye (turban and lateral) of a male C. hageni nymph S to 9 

 mm. long, X I2 °- 



4S4 



