I04 



ENTOMOLOGICAL NEWS. 



[September, 



The movable parts are the antennce and the mouth parts. 

 The compound eyes (fig. i, a) are quite conspicuous, and us- 

 ually are easily seen and recognized as eyes. They are two in 

 number, and are placed one on each side of the head. The sur- 

 face of each compound eye is made up of a large number of 

 hexagonal facets, fitting against each other like the cells of a 

 honey-comb. Each facet is the cornea of a distinct simple eye. 

 The number of facets in the compound eyes of different insects 

 varies from 50 to 30,000 (Comstock). Sometimes the facets are 

 quadrangular (Packard). 



The simple eyes (fig. i, e) are small and not very conspicuous.* 

 They are placed on the top (dorsal* surface) of the head, between 

 the compound eyes. Ordinarily there are 

 three- simple eyes, but their number varies 

 from one to four; they are usually wanting 

 in beetles. Compound eyes are clusters 

 of simple eyes. Lar\ ae have only simple 

 eyes, situated on the sides of the head. 

 During growth they " increase in number, 

 and finally coalesce to form the compound 

 eye, or compound cornea, the surface of 

 which is very convex and protuberant in 

 the predaceous insects, or those requiring 

 an extended field of vision (Packard's 

 Guide)." Usually the compound eyes are 

 referred to as simply "the eyes," while 

 the simple eyes are termed ocelli (singular 

 ocellus) or stemmata (sing, stemmd). 

 The occiput is the rear or base of the head, and articulates 

 with the first segment of the thorax. 



The epicranium (fig. i) is in front of the occiput, and, in gen- 

 eral, forms the top or dorsal portion of the head, but it very often 

 forms part of the sides of the head and even of the under (ven- 

 tral) surface. On account of its extent, names have been given 

 to different parts of the epicranium. The vertex is its topmost 

 (most dorsal) part, t\\^ front ox frons is its most anterior part, the 

 gena, or cheeks, its sides, or lateral parts. The ocelli are usually 

 situated on the vertex. 



Fig. I, Front view of the 

 Head of a Wasp. 



a, a, the compound eyes; 

 b, the clypeus; c, the labrum; 

 d, the mandibles ; e, three 

 ocelli, or simple eyes ; /,/, 

 places of insertion of an- 

 tennae. The letter displaced 

 upon the vertex, / / upon 

 the frons. 



♦When an insect is standing in' natural position, its upper surface is dorsal, its lower 

 surface ventral. 



