THE ANATOMY OF INSECTS. 9 



mum, and clypeus) pertain to the dorsal surface ; and the fourth 

 (gula) to the ventral surface. 



Frequently the sutures between some of these sclerites are obso- 

 lete ; but by studying a series of insects each of these parts can be 

 distinguished. 



The Compound Eyes. In many insects the most striking in appear- 

 ance of the fixed parts of the head are the eyes (3).* These are 

 situated one on each lateral aspect of the 

 head. They are usually nearly hemispherical 

 and of considerable size. When examined with 

 a microscope, they present the honey-comb- 

 like appearance shown in Fii;. 16. Each of 

 the hexagonal divisions of the eye is a cornea 

 of a distinct eye. These large eyes are there- FlG - 

 fore compound. Each of the small eyes of 

 which they are composed is termed an ocellus. Compound eyes are 

 not found in larvae. 



The Simple Eyes. In addition to the compound eyes, many insects 

 -imple eyes (4). These are situated in adult insects on the 

 dorsal aspect of the head between the compound eyes, and in larvae 

 on the Cities of the head. They vary in number in the adult from 

 one to four. The most common number is thn Fig. 15. 



Each simple eye resembles an ocellus of a compound eye. The 

 simp .ire usually termed ocelli; sometimes, stcinwtitii. 



When the term ocelli is used in descriptive works, if there is noth- 

 xt to indicate the contrary, it is almost invariably 



lied to the simpl< and not to the elements of the compound 



In the same way the term eye usually refers to the compound 

 otherwise indicated by the context. 



ifl usually the largest of the three 



sclerites which pertain to the dorsal aspect of the head. It is that sdei ite in 

 h the simple eyes are situated, and which surrounds the compound eyes. 

 It occupies an intermediate position in the d rsal aspect of ti u in^ 



bounded cau'i be occiput iialad by the clypeus. 



i the fact that the epicranium occupies so larije a part of the 1. 

 frequently becomes necessary to speak of jjarticul.tr legions of it in m.; 

 detailed descriptions of insects. Consequently names have been given to 



s are vcr\ These n.mi< 



nis of the 

 us have been applied. Roughly speaking, the 



e Tabular Review at end of dbctusi tul Anatomy. 



lit ions of th '-noting position and direction of parts, see Glossary. 



