230 



COCKROACHES. PHYLUM ARTHROPODA 



that in the male B. orientalis, portions of the terga remain un- 

 covered. The first sternum is rudimentary, and the tenth tergum 

 projects backwards as a plate with a deep notch in its hinder 

 edge. A pair of many-jointed, spindle-shaped anal cerci, which 

 may represent limbs, are attached under this plate, and below 

 it is the anus, between two podical plates or paraprocts, which 

 may represent the sternum of an eleventh somite. In the female 

 the seventh sternum is produced backwards into a large boat- 

 shaped process, which forms the floor of a genital pouch, and in 

 the male the ninth sternum bears a pair of limbs in the form of 



15 



14 



Fig. 165. — A male of the Common Cockroach (P. orientalis) in side view. — From 



Shipley and MacBride. 



I, Antenna ; 2, head ; 3, prothorax ; 4, fore wing ; 5, soft skin between terga and sterna ; 6, sixth abdominal 

 tergum ; 7, split portion of tenth abdominal tergum ; 8, anal cerci ; 9, styles ; 10, coxa of third leg ; 

 II, trochanter ; 12, femur ; 13, tibia ; 14, tarsus ; 15, claws. 



slender, unjointed styles. The genital opening is placed below 

 the anus and is surrounded by a complicated set of processes 

 known as gonapophyses. A pair of stink glands, deterrent to most 

 enemies, opens on the membrane between the fifth and sixth terga. 

 Segments one to eight are limbless. 



LOCOMOTION 



While the insect is walking, three legs are in contact with the 

 ground at one time. On one side the first leg pulls and the third 

 pushes while on the opposite side the second leg acts as a prop. 

 Meanwhile the other three legs are being moved forwards to 

 repeat the process. 



In flight, the hind wings beat in a complicated figure which 

 both supports the body and drives it forwards. They are moved 

 by two sets of muscles — an indirect set, consisting of vertical 

 and longitudinal muscles of the thorax which by alternately 



