12 ELEMENTARY ENTOMOLOGY 



and mosquitoes, the antennae of the sexes are quite different, so 

 that the sexes are readily distinguishable. 



Eyes. On either side of the antennae are found the large com- 

 pound eyes, often forming the larger part of the side of the head, 

 and sometimes, as in the dragon-fly and horse-fly, forming the 

 major portion of the head. The compound eyes are usually oval 

 or circular in outline, and are called compound because, when 

 examined under a lens, they are seen to be composed of large 

 numbers of hexagonal areas, called facets. The number of these 

 facets varies from 50 in certain ants to 4000 in the house-fly and 



FIG. 10. Face of grasshopper 



ant, antenna ; cl, clypeus ; eye, compound eye ; lab, labium ; Ibr, labrum ; Ib.p, labial palpi ; 



mx.p, maxillary palpi ; oc, ocellus 



27,000 in certain sphinx moths. Between the compound eyes, 

 on the front, or vertex, of the head, are two or three small oval 

 or circular simple eyes, called ocelli. Caterpillars and other larvae 

 have no compound eyes, but on either side of the head have a 

 group of from four to six ocelli. In many flies and bees the com- 

 pound eyes of the male are larger and closer together than those 

 of the female, this being due, possibly, to the male's leading a 

 more active life. 



Mouth-parts. The mouth-parts are of prime importance, both 

 from an economic and from a systematic standpoint. Upon their 

 structure depends the kind of insecticide which may be effectively 



