574 ZOOLOGY SECT. 



between the head proper and the thorax, is covered for the most 

 part by a thin flexible cuticle, but there are supporting it eight 

 thickened and hardened patches the cervical sclcrites (cerr.). 



Each of the three segments of the thorax known respectively 

 as prothorax, mesothorax, and mctatlwrax 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 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. Attached to 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. 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. 



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, tne 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 placed 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 

 of antennae probably correspond to the antennules of the Crayfish 



