24 ENTOMOLOGY 



cuticula ; though authors are not agreed as to the details of the develop- 

 ment. 



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 holometabolous insects, in some 



FIG. 34. Skull of a grasshopper, Dissos- 

 teira Carolina. 0, occipital foramen; t, t, 

 anterior arms of tentorium. 



FIG. 35.- 



-Head of a gyrinid beetle, Dineutus, 

 to show divided eye. 



generalized forms (as Collembola) and in parasitic insects. The com- 

 pound eyes (Fig. 40) are convex and often hemispherical, though their 

 outline varies greatly; thus it may be oval (Orthoptera) or triangular 

 (Notonecta), while in the aquatic beetles of the family Gyrinidse (Fig. 35) 

 each eye has a dorsal and a ventral lobe, enabling the insect to see upward 



FIG. 36. Agglomerate eyes of a male coccid, 

 Leachia fuscipennis. After SIGNORET. 



11B1I 



FIG. 37. Facets of a compound eye of 

 Melanoplus. Highly magnified. 



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 agglomerate 

 type of eye (Fig. 36) are commonly more or less hexagonal (Fig. 37), as 

 the result of mutual pressure. These facets are not necessarily equal in 



