EXTERNAL PARTS OF A COCKROACH 7 



Cut off the head with a pair of scissors. Holding it between 

 the finger and thumb, pass the blade of a scalpel behind the 

 labrum and the mandibles. The blade will lie in the mouth 

 from side to side, the labrum and mandibles being in front of 

 It, and the other mouth-parts behind. Press the blade until 

 It cuts through the head, dividing it into a fore and hind half 

 Cut off another head. Turn up the hind surface, and pass 

 the- scalpel beneath a small flap, the labium, which hangs 



Fig. 3. — Side of head 

 of cockroach, oc, eye ; 

 ge, gena ; w/«, man- 

 dible. X 10. 



Fig. 4. — Back of head of cockroach, ca, 

 cardo ; st, stipes ; ga, galea ; /a, lacinia ; 

 pa^ palp ; sfn, submentum ; ;«, mentum ; 

 i>g^ paraglossa. X lo. 



down behind the mouth. Grasping this between the scalpel 

 and the thumb, strip it off in an upward direction. From the 

 second head take off the two maxillse, which, now that the 

 labium is gone, are exposed on the hinder surface. Place 

 the bisected head, the labium and the two maxillae in a small 

 bottle containing a solution of caustic potash, say five per cent. 

 Leave this to a future day, when the parts can be mounted 

 and examined. 



The thorax consists of three segments. The fore thoracic 

 segment, or prothorax, has the tergum prolonged forwards 



