The In/ago. 49 



parts, the labrum and the labium, move vertically 

 Between them on each side are two pieces, the 

 mandibles (Fig. 21, C; above and the iiiaxilUc below 

 (Fig. 21, B), which move horizontally. The mandibles, 

 which are armed with jagged tooth-like indentations, 

 are the parts chiefly concerned in crushing the food. 

 By some, and probabK' correctl}-, the side j^ieces of the 

 labium (Fig. 21, A, s) are looked upon as a second 

 pair of maxillai, but we are only concerned with their 

 function, that the}' act as parts of the lo\\er lip. In the 

 interior of the mouth, attached to the labium, is the 

 lingua, or tongue. When full}' open, the orifice of the 

 mouth is very large, an obvious ad\antage to an insect 

 that catches its prey upon the wing. 



Behind the head, and in some species quite hidden 

 within the cavity mentioned above, is the prothorax 

 (Fig. 22, A and D). The pro-sternum, or ventral 

 surface of it, is small, but bears the fore-legs ; the jDro- 

 notum, or dorsal surface, somewhat larger, is in the 

 Agrioniiicc sometimes sufficiently varied to assist in 

 differentiating the species. The meso-thorax alwa}'s 

 greatl}- overlaps the meta-thorax — so much so that the 

 meso-notum and meta-notum are pushed quite back, 

 and the attachments of both pairs of wings are behind 

 those of the mid- and hind-legs. Especiall}- is this the 

 case in the Zygopterides. 



Three tarsal joints are found in the legs of all British 

 Dragonflies, the basal one being invariably the smallest 

 (Fig. 22, C). The most noticeable point in connection 

 with the legs is the double series of long bristles 

 which adorn them, and which seem to perform a very 

 important dut}'. It will quickl}- be noticed that a 



E 



