236 ARTHROPODA [CH. 



L-slmped hinge which, when opened out, protrudes the jaw. The 

 outer portion of the first maxilla is many-jointed and is sensory in 

 function, constantly touching and testing the ground as the animal 

 moves about. It is called the maxillary palp. 



The second maxillae are united across the median line and thus 

 constitute a fold or plate called the labium, which bounds the 

 mouth behind as the labrum bounds it in front (Fig. 98, C). Each 

 half may be resolved into elements similar to those of the first 

 maxillae, the fused basal joints of the pair of appendages form the 

 mentum and sub-inentum, the galea being represented by the 

 paraglossa, whilst the inner gnathobase corresponds with the 

 lacinia and is termed the ligula. As in the case of the first 

 maxilla the outer joints of the appendage which have a tactile 

 function are termed the labial palp. 



The thorax is built up of three segments, the pro-, meso- and 

 met a- thorax. The skeleton of each segment con- 

 sists of a dorsal hard piece, the tergum, united 

 with a corresponding ventral piece, the. sternum, by a soft in- 

 tervening pleural membrane. The tergum of the first thoracic 

 segment is clearly visible, but the meso- and meta-terga are 

 concealed by the wings. The two pairs of wings are formed by 

 folds of the skin arising from the terga of the meso- and meta- 

 thorax respectively, and in a state of rest conceal the dorsal surface 

 of the animal behind the prothorax. The front pair are termed 

 elytra ; they are hard and horny, one overlaps the other, and they 

 probably serve more as protectors to the delicate hind wings than 

 as organs of flight. The posterior wings are thin and membranous 

 and are of greater area than the elytra, and they constitute the 

 effective organs in the rare flight of the cockroach. At rest they 

 are folded like a fan and concealed by the elytra. In Stylopyga 

 orientalis the wings as is not uncommon amongst Insects are 

 rudimentary in the female. 



The ventral plate or sternum of each thoracic segment bears a 

 pair of legs by means of which the cockroach scuttles rapidly about. 



Each leg consists of a number of joints, via., a thick flat coxa 

 applied to and articulating with the sternum ; a minute triangular 

 joint, the trochanter; a stout joint called the femur; a more 

 slender one termed the tibia, armed with spines; then a piece con- 

 sisting of five short joints called the tarsus, with a whitish hairy 

 patch under each joint which acts as a sole; and finally a pair of 

 terminal claws (15, Fig. 97, B). These names, as is too often the case 



