ANATOMY AND PHYSIOLOGY eye 
which produces the external cuticula; though authors are not 
agreed as to the details of the development. 
Eyes.—The eyes are of two kinds—simple and compound. 
The latter, or eyes proper, conspicuous on each side of the 
head, are of common occurrence 
FirGaaas 
except in the larvae of most holo- 
metabolous insects, 11 some gene- 
ralized forms (as Collembola) and 
in parasitic insects. The compound 
eyes (Fig. 40) are convex and often 
hemispherical, though their outline 
varies greatly; thus it may be oval 
(Orthoptera) or triangular (Noto- 
necta), while in the aquatic beetles , 
of the family Gyrinidz ( Fig. 35 ) Head of a gyrinid beetle, Dineu- 
Pas tus, to show divided eye. 
each eye has a dorsal and a ventral 
lobe, enabling the insect to see upward and downward at the 
same time; so also in Oberea and other terrestrial beetles of the 
same family. Superficially, a compound eye is divided into 
minute areas, or facets, which though circular in the agglom- 
Fic. 37. 
Agglomerate eyes of a _ male Facets of a compound 
coccid, Leachia  fuscipennis.— eye of Melanoplus. 
After SIGNORET. Highly magnified. 
erate type of eye (Fig. 36) are commonly more or less hex- 
agonal (Fig. 37), as the result of mutual pressure, These 
facets are not necessarily equal in size, for in dragon flies the 
dorsal facets are frequently larger than the ventral. In diam- 
