MOVEMENT 65 



cardo, and raises the maxilla. From the tentorium a broad 

 strap-like muscle (G) passes to the stipes which it pulls, when 

 contracting, towards the centre of the mouth ; this is the 

 adductor of the stipes (and necessarily of the lobes carried 

 by it) which it moves on the hinged articulation with the 

 cardo. From within the stipes arise two long, thick tapering 

 muscles (A, B), one the adductor of the lacinia and the other 

 of the galea to the bases whereof they are respectively 

 attached, the action of the latter being aided by another 

 muscle arising from the tentorium. Two smaller muscles 

 (D, E) passing from the inner edge of the stipes to the 

 upper and lower edge of the palpiger are respectively the 

 adductor and abductor of the palp as a whole, while the 

 individual segments of that leg-hke region are worked by 

 slender muscles concealed within it. Thus the movements 

 of the palp in testing objects over which the insect walks, 

 as well as the action of the maxillary laciniae or blades in 

 breaking up foodstuffs into finely divided particles are 

 brought about. 



The arrangement and mode of working of the head 

 muscles are necessarily strongly modified in the case of 

 jaws adapted for piercing and sucking. As an example 

 we may take the jaws of a plant-bug such as Lygus 

 pabulinus described in detail by P. R. Awati (1914)- 

 The mandibles and maxillae of insects of this order are 

 elongate piercing stylets working to and fro in the dorsal 

 groove of a jointed beak which is the modified labium. 

 For the puUing back of these piercing jaws, there are 

 retractor muscles which arise from chitinous rods in the 

 dorsal region of the head-capsule, and are inserted into 

 the swollen bases of the mandibles and maxillae respec- 

 tively (Fig. 24A, r, rx). The jaws are thrust out, so 



Fig. 23. — Maxillae of Australian Cockroach {Periplaneta australasiae). 

 A, right maxilla from behind ; B, left maxilla from front, car, cardo ; 

 St, stipes ; la, lacinia ; ga, galea ; p, palp ; m, articulation of lacinia. 

 ten, tentorium. Muscles : A and Q, adductors of lacinia ; B, adductor of 

 galea ; D, adductor, and E abductor of palp ; H, L, N, T, segmental 

 muscles of palp ; G, adductor of stipes ; P, elevator, and W, depressor 

 of cardo. X 24. After J. Mangan {Proc. R. I. Acad, xxvii, 1908). 



F 



