622 ZOOLOGY 



SECT. 



ramus or endopodite, and an external ramus or exopodite. The 

 former consists of two parts : an inner, pointed, hard blade — the 

 lacinia (mi.), and an outer, softer, more elongated— the galea (me.). 

 The exopodite forms a palp, the maxillary palp (mn.), consisting 

 of five podomeres. Behind these are the second maxillae, which 

 are reducible to the same type, but which have their two basal 

 segments (those of the protopodites) united together in the 

 middle line to form two median sclerites, known respectively as 

 mentum (??i.) and momentum (sm), so that the two appendages 

 form a sort of lower lip called the labium. The endopodites taken 

 together constitute what is termed the ligula ; each is divided into 

 two parts like the endopodite of the first maxillae. The exopo- 

 dites form three-jointed palps, the labial palps (pi.). 



The neck, or narrow region between the head proper and the 

 thorax, is covered for the most part by a thin flexible cuticle, but 

 supporting it are eight thickened and hardened patches — the 

 cervical sclerites (cerv.). 



Each of the three segments of the thorax — known respectively 

 as prothorax, mesothorax, and metathorax — is covered over dorsal ly 

 by a chitinous plate — the tergum, and ventrally by another — the 

 sternum. The tergum and sternum of each segment are distinct 

 from one another, not united into a continuous sclerite as in the 

 Crayfish. The tergum of the prothorax is larger than that of the 

 other two segments, and overlaps the neck above. Attached to 

 the anterior border of the tergum of the mesothorax in the male 

 are the anterior wings or elytra — a pair of thick opaque plates, 

 which, in their ordinary position, extend backwards over the 

 abdomen to some little distance beyond its extremity. Articulating 

 with the tergum of the metathorax are the posterior wings — a pair 

 of extremely delicate membranous expansions, which, when at rest, 

 are folded up longitudinally, like a fan, under the elytra. In the 

 female of P. orientalis the wings are only represented -by small 

 vestiges. Attached to the sternum of each segment of the thorax 

 is a pair of legs. Each leg consists of a stout flattened proximal 

 podomere or coxa ; a small second, or trochanter ; a third, the femur, 

 similar to the coxa but narrower ; a fourth slender and spinose, the 

 tibia ; and finally the tarsus or foot, composed of six very short 

 segments provided ventrally with patches of setae to give adhesive 

 power; the last segment (pulvillus)' is armed in addition with a 

 pair of claws (Fig. 491). 



Of the segments of the abdomen the most posterior are over- 

 lapped by those just in front. Each is enclosed in a dorsal tergum 

 and a ventral sternum, both of which are thinnish and flexible — 

 the terga and sterna of succesive segments overlapping one another 

 from before backwards. The eighth and ninth terga are hidden 

 from view by being overlapped by the seventh. The tenth is 

 produced backwards into a thin flexible plate, the posterior border 



