STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 



Epicranium 



(a) Vertex or crown, the summit of the head, often 



with ocelh. 



(b) Front or face. 



(c) Genae or cheeks. 



(d) Occiput, which surrounds the posterior opening of 

 the skull. 



(e) Clypeus, to which the labrum or upper lip is attached, 

 (/) Gula, to which the labium or lower lip is attached 



(see Figs. 2 and 3). 



ForeiV/ng ,v Mmdmn< 



Fig. I. — Diagram showing the position and arrangement of the principal organs 

 and appendages of an insect. Ant., Antenna; Br., brain; Ao., aorta; LM., leg mus- 

 cles originating in the thorax; DM., dorsal longitudinal muscles of abdomen; H., 

 heart; MT., Malpighian tubules; ED., efferent duct (oviduct or vas deferens) of 

 reproductive system; G., gonad (ovary or testis); Cer., cercus; A., anus; Gon., 

 gonapophyses; CD., common duct (vagina or seminal vesicle) of reproductive sys- 

 tem; VG., ganglia of ventral nerve chain; Tr., tracheal trunk showing origin and 

 distribution of ventral, dorsal and visceral tracheal branches; VM., ventral longi- 

 tudinal muscles; TS., tergo-sternal muscles; Cox., coxa; Tro., trochanter; Fetn., 

 femur; Tib., tibia; Tar., tarsus; SGL, salivary gland; SD., salivary duct; SG., sub- 

 cesophageal ganglion; Ph., pharynx; S., stomodfEum or fore intestine; M., mesen- 

 teron or mid intestine; P., proctodaeum or hind intestine. 



In addition there is in the head an internal chitinous skeleton 

 called the tentorium, which acts as a supporting structure. It varies 

 in form in different insects. but consists essentially of a central plate 

 and two pairs of arms connecting with the skull. (The tentorium 

 may be isolated by boiling the head in a 5 per cent, solution of caustic 

 potash for ten minutes.) 



Mouth-parts. — In general there are three types of mouth-parts: 

 mandibulate, present in the generalized orders and in the Orthoptera, 



