ENTOMOLOGY IN OUTLINE STRUCTURE OF INSECTS. 



15 



as the dragon-fly, the house-fly, and others, they form the greater part 

 of the head. The eye of an insect is immovable, fast in its socket. It 

 is hemispherical or curvilinear in form, and covered with facets or flat 

 surfaces. They are called compound eyes, and are of many colors— blue, 

 black, emerald green, or deep golden, as in the lace-winged fly. Really, 



FIG. 8. Agglomerate eyes of a 

 male coccid, Leachia fngci- 

 pcnnis (After Signoret.) 



FIG. 9. Facets of a com- 

 pound eye of Metano- 

 jjIus. Highly magnified. 



each facet is a separate eye, hexagonal in 

 shape, with a cornea, lens, pigment-coating, 

 and nervous filament. The facets face in 

 every direction and enable the insect to see fig. lo. Portion of compound eye 

 on all sides with greater ease than if they ai section, c, cornea ; z, iris pig- 

 were single lensed and movable. In some ment; ;«, nerve fibers ; «c, nerve 

 ,-, r . ±\ cells; ?-, retinal pigment; i, tra- 



cases these facets are very numerous, the eye ^^^^^ (After Hickson.) 



of a small beetle, the Mordella, having over 



25,000, the common swallow-tailed butterfly, the Papilio, having 17,000, 



the dragon-fly 12,000, the house-fly 4,000, while the eyes of some ants 



are limited to 50. Besides these compound eyes, most insects have two 



or three simple eyes, 

 known as ocelli or 

 stem ma ta. These 

 are usually arranged, 

 in triangular form 

 (thus .*.), and are 

 round and convex 

 in shape. These ex- 

 tra eyes are not pres- 

 ent in all insects, 

 nor are their exact 

 functions known. 



They are possessed of great refractive power and are supposed to be of 



use in the examination of near-by objects. 



Month. — The mouth is a very complicated piece of mechanism, 

 and is furnished with various organs, enabling the insect to take its 

 nourishment as its habits require. There are two general classes of 



FIG. 11. OcuUi and compound eyes of the honey-bee {Apis 

 vicUifera). A, queen ; B, drone. (After Cheshire.) 



