

ANATOMY AND PHYSIOLOGY 



easily recognized as being the sclerite to which the upper lip, or labrum, 

 is hinged, though the clypeus is not invariably delimited as a distinct 

 sclerite. In certain insects a transverse suture divides the clypeus 

 into an anteclypeus and a postclypeus. The cheeks of an insect are 

 known as the gence, and post-gena sometimes occur. On the under side 

 of the head is the gula, which bears the under lip, or labium. That part 

 of the skull nearest the prothorax is termed the occiput; usually it is not 

 delimited from the epicranium, though in some insects it is continuous 

 with the post-genae to form a distinct sclerite. The occiput surrounds 

 the opening known as the occipital foramen, through which the cesopha- 



oc 



B 



FIG. 34. Skull of a grasshopper, Melanoplus differentialis. a, antenna; c, clypeus; e, 

 compound eye; /. front; g, gena; I, labrum; Ip, labial palpus; ra, mandible; mp, maxillary 

 palpus; o, ocelli; oc, occiput; pg, post-gena; v, vertex. 



gus and other organs pass into the thorax. The membrane of the 

 neck in Orthoptera and some other insects contains small cervical 

 sclerites, dorsal, lateral or ventral in position; these, in the opinion of 

 Comstock, pertain to the last segment of the head. Besides those 

 described, a few other cephalic sclerites may occur, small and incon- 

 spicuous, but nevertheless of morphological importance; for example, 

 ocular or antennal sclerites, bearing the eyes or the antennae, respec- 

 tively; and the trochantin of the mandible, situated between the mandi- 

 ble and gena. 



Tentorium. In the head is a chitinous supporting structure known 

 as the tentorium. This consists of a central plate from which diverge 

 either two or three pairs of arms (anterior, posterior and dorsal) extending 



