66 



THE BIOLOGY OF INSECTS 



mx 



Fig. 24A. — Cross-Section through Head of Plant-bug (Lygus pabu- 

 linus) ; Ph, pharynx ; dy its divaricator muscle ; g, gullet ; ps, salivary 

 pump ; mp, its muscle ; sd, salivary duct ; r, retractor, and p, protractor 

 muscles of mandible {mn) ; rx and px, retractor and protractor of maxilla 

 {mx) ; /, labial muscle ; b, brain ; s, sub-oesophageal ganglion ; «, nerve- 

 commissure ; o, taste-organs. X 200. After P. R. Awati, P. Z. S. 1914. 



as to perforate the plant tissues and procure a supply of 

 food-sap by the contraction of protractor muscles, which 

 arise from the frontal ventral head-skeleton, and are in- 

 serted, in the case of the maxillary protractors {px)^ directly 

 into the swollen bases of the jaws, but for the mandibular 

 protractors {p) into transverse chitinous rods attached to 

 the bases of the mandibles, and therefore pulling these as 

 by the agency of levers. The labial beak, in which the 

 mandibles and maxillae are thus pulled in or out, can be 

 moved forwards and backwards by elongate muscles which 

 pass from the dorsal wall of the prothorax to the front 

 and hind aspect of the base of the terminal segment of 



