XXXll INTRODUCTION. 



muscular structure, the colon or rectum, which is usually filled with ejecta 

 and terminates at the anal valve. 



EXTERNAL STRUCTURE. 



There are always present a distinctly separated Head, hearing a pair of 

 elongate antennae, 'J'horax and Abdomen, three pairs of Legs and usually 

 two pairs of membraneous Wings. 



The Head, viewed from above, is transverse or quadrate ; from in front, 

 it becomes more or less strongly narrowed towards the mouth and is always 

 sculptured with punctures or reticulations. The eyes are very large an-d 

 occu[)y nearly the whole anterior side of the head. The vertex bears three 

 ocelli, situated triangularly, and behind them is the occiput sloping to the 

 collar. Between the ocelli and the insertion of the antennae is the frons, 

 usually bearing glabrous scrobes upon its anterior portion ; below these is 

 the face, known centrally as the epistoma, its apical margin being discreted 

 from the clypeus, which extends across the whole front of the head, by a 

 usually present transverse impression terminating on either side in a fovea. 

 The apical margin of the clypeus is usually truncate, or sub-bisinuate, though 

 occasionally dentately reflexed or rotund. The cheeks, which lie between 

 the apical extremity of the eyes and the base of the mandibles, and the 

 temples, behind the eyes, are more or less broadly buccate, and the former 

 vary in their length according as the eyes approach or recede from the 

 mandibles, which are broader basally than apically, and sometimes as 

 broad as the cheeks are long. The apex of the mandibles, which lie 

 folded the one upon the other across the front of the clypeus, is usually 

 bidentate, the upper in most cases being much longer than the lower tooth, 

 but in some instances the teeth are of equal length or the lower is wanting. 

 Between the apex of the clypeus and the mandibles, the labrum is more.or 

 less visible, rotund and ciliated. The two pairs of palpi, the maxillary and 

 the labial, are elongate ; the former consists of five usually cylindrical, the 

 latter of two triangular and two cylindrical, joints. The mentum, ligula, 

 hypo-pharynx, &c., are not alluded to in descriptions. 



The Antennae are inserted between the eyes in the front of the head. 

 They are multiarticulate, as many as seventy joints being found in certain 

 genera, while in others the number diminishes to fourteen. The scape 

 consists of the two basal joints (the radicula or basal joint not being 

 mentioned in descriptions). The first of these is oval or shortly cylindrical, 

 with an incision on its under side, in which is inserted the second joint or 

 pedicellus, having its apex always free, but shorter than the scape proper. 

 Next follows a minute joint, termed the annellus, which, with the re- 

 mainder of the antennae, constitutes the flagellum. The joint immediately 

 following the annellus is known as the post-annellus. During life the 

 antennae are porrect and held while in repose straight forward, not recurved 

 beside the body as in most Orders. After death they very often become 

 convoluted and spirally coiled, as described by the older authors. 



The Thorax consists of three distinct sections : — that nearest the head 

 is the prothorax, bearing the front pair of legs ; the middle section is the 

 mesothorax bearing the intermediate pair of legs and anterior pair of 

 wings ; the last section is the metathorax bearing the hind pair of legs 

 and posterior pair of wings. The disc of these sections is known as the 



