228 COCKROACHES. PHYLUM ARTHROPODA 



There is some evidence that the secretion of the hormone 

 is itself determined by events in the outer world, acting via 



the sense organs and nervous 



t!cr. sut. 

 /\ '.' J'en. 



system. 



'uiL 



\--et/^ 



THE HEAD 



lb 



m. 



lb. p. 



Fig. 163. — The head of a cockroach 

 seen from in front. 



at.. Antenna; dp., clypeus ; ecr., epicranium; 

 eye ; fen., fenestra ; fr., frons ; gen., 

 gena ; Ibm., part of the labium ; lb. p., 

 labial palp ; Ibr., labrum ; md., mandible, 

 mx., part of the maxilla; mx.p., maxillary 

 palp ; sui., sutures. 



and are shown in Fig. 164 



The head (Fig. 163) is short 

 and deep. Seen from in front it 

 has a pear-shaped outHne, with 

 the narrow end downwards. Its 

 armour consists of several pieces — 

 two epicranial plates side by side 

 above, two genae at the sides 

 below the eyes, a frons and clypeus 

 in front. A labrum is hinged on 

 to the clypeus below ; its lining 

 is known as the epipharjmx. The 

 appendages of the head are paired, 

 and in Table III. 



TABLE III 

 Head Appendages of a Cockroach 



THORAX 



The head is joined by a soft neck to the thorax. This consists 

 of three segments — the prothorax, mesothorax, and metathorax. 

 Each has a tergum or notum above and a sternum below, joined 

 to one another at the sides by membrane in which lie small 

 sclerites — the pleura — which are really basal podomeres of the 

 legs. The pronotum is the largest and projects in front so as to 

 hide the neck. Each sternum bears a pair of legs. The shape of 



