TEXT-BOOK OF ENTOMOLOGY 



THE HEAD AND ITS APPENDAGES 

 a. The head 



While the head is originally composed of probably not less than 

 six segments, these are in the adult insect fused together into a cap- 

 sule or hard chitinous box, the epicranium, with no distinct traces of 

 the primitive segments. The head contains the brain and accessory 

 ganglia, the mouth or buccal cavity, also the air-sacs in many winged 

 forms, and gives support to the external organs of sense, the 



antennae, and to the buccal appendages, 

 the larger part of the interior being 

 filled with the muscles moving these 

 structures. The solid walls of the head 

 serve as a lever or support for the 

 attachment of these muscles, especially 

 those of the mandibles. Thus there is 

 a correlation between the large size of 

 the mandibles of the soldier white ants 

 and ants, the head being correspond- 

 ingly large to accommodate the great 

 mandibular muscles. The other extreme 

 is seen in the larva of Necrophilus 

 (Fig. 24), with its long slender neck 

 and diminutive head. 



The clypeus. This is that part of 

 the head situated in front of the epi- 

 cranium, and anterior to the eyes, form- 

 ing the roof of the posterior part of the mouth, and is, as embryology 

 shows, probably a tergal sclerite. It varies greatly in shape and size 

 in the different orders of insects. It is often divided into two parts, 

 the clypeus posterior and clypeus anterior, or which may be desig- 

 nated as the post- and ante-clypeus (Figs. 29, JB). 



The labrum. The " upper lip " or labrum is an unpaired flap-like 

 piece hinged to the front edge of the clypeus, and may be seen to 

 move up and down when the insect moves its mandibles. It forms 

 the roof of the anterior part of the mouth (Figs. 69, 74), and its inner 

 side is lined with a soft membrane, usually provided with hairs and 

 sense-papillae or cups, forming the epipharynx. 



The labrum is more or less deeply bilobed, especially in caterpil- 

 lars and in adult Staphylinidae, and has been thought by some 



FIG. 24. Presumed larva of Nem- 

 optera (tfecrophilus arenarius), 

 Pyramids of Egypt. After Koux, 

 from Sharp. 



