606 ZOOLOGY 



SECT. 



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 metathorqx is covered over dorsally 

 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 setse to give adhesive 

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

 pair of claws (Fig. 498). 



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 successive 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 

 of which presents a deep notch ; below this is the opening of the 

 anus, at the sides of which are a pair of small hard plates the 

 podical plates ; at the sides of the tergum are a pair of many- 

 jointed palp-like bodies the cerci. The sternum of the first 

 abdominal segment is rudimentary. In the male that of the ninth 

 bears a pair of short styles. In the female the sternum of the 

 seventh is very much more prominent than in the male. The 

 genital aperture is situated on the ventral aspect of the posterior 

 extremity of the abdomen beneath the anal opening. 



When compared with the Crayfish, as regards the external 

 anatomy, the Cockroach is found to differ (1) in the arrangement 

 of the segments into regions ; (2) in the form and position of the 

 appendages. The head and thorax together correspond to the 

 cephalothorax of the Crayfish, but comprise fewer segments ; the 

 abdomen contains a larger number of segments. The single pair 



