BLEPHAROCEEID.E. 



149 



the subject of study by more than one autbor. The usual sexual 

 distinction in the comparative width of the frons, which obtains in 

 a great many families of Diptera, does not hold good in the 

 BLEPHABOCEBID;E. The head is usually dichoptic in both sexes, 

 but occasionally it is holoptic in one or both sexes. The eyes 

 " are usually bisected by an unfacetted cross-band or line 

 separating each eye into two fields, an upper and a lower one ; 

 the upper composed of larger and less pigmented ornmatidia (large 

 and brown facets) ; the lower composed of smaller and more 

 strongly pigmented ornmatidia (small black facets). In a few 

 species the eyes are bisected only in one sex. Three rather large 

 ocelli are present " (Kellogg). The upper eye faces dorsally and 

 is composed of large facets, the lower one faces ventrally, anteriorly 

 and laterally, and is composed of much smaller facets. Radical 

 structural differences exist in addition between the upper and 

 lower eye.* 



Fig. 13. Mouth-parts of a Blepharocerid, Bibiocephala 

 doanei, Kellogg (after Kellogg). 



The mouth-parts are complex, elongated, " the female having in 

 addition to labium and maxillae, slender flattened elongate, saw- 

 like mandibles ; the males are without these mandibles. Both 

 sexes have a slender elongate labruin-epipharynx, a similar slender 

 elongate hypopharynx, a pair oE slender blade-like maxillae, with 

 5-segmented palpi, and labium with slender elongate basal sclerite, 

 and a pair of free fleshy terminal lobes without pseudotracheae and 

 with palpi " (Kellogg). 



* For studies on eyes of this divided character in other groups of animals, 

 reference can be made to " The divided eyes of Arthropods " by Kellogg, Zool. 

 Anzeig. (1898). Zimmer (Zeits. f. wiss. Zool. Ixiii, pp. 236-262, 1898) on the. 

 eyes of EPHEMERID-E may also be consulted. 



