ANATOMY AND PHYSIOLOGY 



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 

 except in the larvae of most holo- 

 metabolous insects, in 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 Gyrinidse (Fig. 35) 

 11 111 1 



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- 



Head of a gyrinid beetle, Dineu- 

 * us > to show divided eye. 



FIG. 36. 



FIG. 37- 



Agglomerate eyes of a male 

 coccid, Leachia fuscipennis. 

 After SIGNORET. 



Facets of a compound 

 eye of Melanoplus. 

 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- 



