IO AN INTRODUCTION TO ENTOMOLOGY. 



front (2a) is the cephalic portion of the epicranium (Fig. 17). It is bounded 



cephalad by the clypeus, and laterad by the eyes 

 and gense. The vertex (2b) is the remaining part 

 of the dorsal portion of the epicranium ; it ex- 

 tends from between the eyes to the occiput. By 

 many writers the term vertex is used in a vague 

 manner to indicate the summit of the head. 

 The gence (2c) or cheeks are the lateral portions 

 Tig. I7 .-Head of locust. of the epicran ; um> t h ose par ts which are usually 



ventrad of the eyes and caudad of the mandibles. In many insects a distinct 

 suture extends cephalad from each compound eye, separating the front from 

 the gense. 



The Occiput. — The occiput (1) is that part of the dorsal wall of the head 

 which is articulated with the cephalic margin of the thorax (Fig. 18). In many 



Fig 18.— Dorsal aspect of head of Harfalus. Fig. 19.— Ventral aspect of head of Har/atus. 



insects it is a distinct sclerite ; in others it is not distinguishable from the epi- 

 cranium. 



The Clypeus. — The clypeus (5) is the cephalic part of the dorsal portion of 

 the fixed parts of the head. It is bounded caudad by the epicranium, and 

 gives attachment cephalad to one of the movable parts of the head, the labrum 

 or upper lip. The clypeus is typically composed of two sclerites. When these 

 are distinct they are designated as the ante-clypeus and post-clypeus respectively. 



The Gula. — The gula (6) is the only one of the fixed parts of the head that 

 is confined to the ventral aspect (Fig. 19). It is bounded laterad by the lateral 

 parts of the epicranium and occiput ; and extends caudad to the caudal border 

 of the head. Cephalad it gives attachment to one of the movable parts of the 

 head, the labium or lower lip. 



The Movable Parts of the Head. 



Under this category are classed a pair of jointed appendages 

 termed the antennae, and the organs known collectively as the mouth- 

 parts. 



The Antennce. 



The antennce (7) are a pair of jointed appendages, inserted in the 

 head in front of the eyes or between them. They vary in form. 

 In some insects they are thread-like, consisting of a series of similar 

 segments ; in others certain segments are greatly modified in form. 

 In the beetles of the genus Collops the antennae bear a curious articu- 

 lated appendage arising from near the base of the third segment.* 



* Horn, Trans. Am. Ent. Soc, III. p. 79, with figure. 



