STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 7 



which is the conspicuous median portion terminating in a large labellum 

 (Fig. id). The mandibles are flat and sword-Hke; the maxillae are 

 narrower, but with broad conspicuous palpi; the hypo pharynx and 

 labrum-epipharynx are also narrow and lancet-like. 



ad.md. 



depJb. 



Pig. 9. — Front of head of Gryllus pennsylvanictis with face and vertex removed. 



Upper Figure. — Epic, Epicranium; Ad., prd.. Id., dilator muscles of the pharynx; 

 Md., mandible; Ph., pharynx. 



Lower Figure. — Longitudinal dorsoventral section through the head of Gryllus 

 pennsylvanictis. prd., prd. 2, prd.3, pstd., Vd., Dilators of the pharynx; Oc, ocellus; 

 Ad.md., adductor of the mandible; Dep.hyp., depressor of the hypopharynx; Hyp., 

 hypopharynx; r.hyp., retractor of the hypopharynx; ap.lb., apodeme of the labium; 

 r.hyp., retractor of the hypopharynx; Jl.st., flexor of the stipes; T.C., central plate 

 of the tentorium. 



Mouth-parts oj Mosquito. — The mouth-parts are similar in number 

 to those of the horse fly but they are more bristle-like (Fig. 11). 



Mouth-parts of the House-fly. —When the head of a living house-fly is 

 pinched between the thumb and finger the mouth-parts are protruded 

 to their full length. They constitute a soft "proboscis" enlarged at 



