ENTOMOLOGY 



FIG. 34- 



mit of the head, is the region known as the vertex; it 

 often bears ocelli. The clypeus is 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. The cheeks of an insect are known as the gence, 

 and post-genes 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 occi- 

 put; usually it is not delimited from the epicranium, though 

 in some insects it is continuous with the post-gense to 

 form a distinct sclerite. The occiput surrounds the opening 

 known as the occipital foramen, through which the oesophagus 



and other organs pass into 

 the thorax. The membrane 

 of the neck in Orthoptera 

 and some other insects con- 

 tains small cervical sclcrites, 

 dorsal, lateral or ventral in 

 position; these, in the opin- 

 ion of Comstock, pertain 

 to the last segment of the 

 head. Besides those de- 

 scribed, a few other cephalic 

 sclerites may occur, small 

 and inconspicuous, but nev- 

 ertheless of considerable 

 morphological importance. 

 Tentorium. In the head is a chitinous supporting struc- 

 ture known as the tentorium. This consists of a central plate 

 from which diverge two pairs of arms extending to the skull 

 (Fig. 34). The central plate lies between the brain and the 

 subcesophageal ganglion and under the oesophagus, \vhich 

 passes between the anterior pair of arms. The tentorium 

 braces the skull, affords muscular, attachments and holds the 

 cephalic ganglia and the oesophagus in place. It is not a true 

 internal skeleton, but arises from the same ectodermal layer 



Skull of a grasshopper, Dissosteira Caro- 

 lina, o, occipital foramen; t, t, anterior 

 arms of tentorium. 



