174 



THE BOOK OF NATURE STUDY 



-a, 



'b 



the pulvillus, which produces a gluey substance to enable the 

 insect to retain its hold on sloping or even on vertical objects. 

 The abdomen is much flattened, and is softer than the thorax. It 

 is composed of ten segments, but the hinder are telescoped within 



one another, so that in the female 

 only eight are obvious from the dorsal 

 side, those concealed from view 

 being the 8th and Qth. The dorsal 

 plate of the tenth is prolonged 

 backwards, and is deeply notched 

 posteriorly ; to its sides is attached a 

 pair of short, jointed rods, the cerci 

 which probably function as tactile 

 organs. The ventral plate of the 

 gth segment bears in the male a 

 pair of short styles, and by these the 

 young wingless males may always 

 be distinguished from females ; while 

 that of the 7th is in the females 

 produced backwards into a large 



boat-shaped structure in which the egg-capsule is moulded. The 

 intersegmental membranes, and those between the several dorsal 

 and ventral plates, are very thin and flexible. In that between 

 the 5th and 6th segments there is situated dorsally a pair of 

 sunken glands, from which is emitted a sticky fluid of peculiarly 

 disagreeable odour. It is to these glands that the cockroach 

 owes its evil scent. The respiratory openings (stigmata) are 

 twenty in number, ten on each side, in the thin membranes 

 between the dorsal and ventral plates : one pair lies between 

 the pro- and mesothorax, one between the meso- and metathorax, 

 and the remainder in the first eight segments of the abdomen. 

 From these openings air is conveyed throughout the body by 

 tracheal tubes, which are fine, much branched inward extensions 

 of the external covering of the body. 



The digestive system of the cockroach can be exposed without 

 much difficulty if the specimen be fastened down on a weighted 

 sheet of cork, or embedded in melted paraffin wax poured into a 

 small dish, and then dissected under water. The dorsal plates 



FIG. 65. Leg of cockroach, a, coxa 

 b, trochanter ; c, femur ; d, tibia 

 e, tarsus. 



