536 HEMIPTERA CHAP. 



maxillae and labium of mandibulate Insects. This point has 

 recently been . discussed by Marlatt l and by Heymons. 2 From 

 the latter we gather that the mode of growth is peculiar by the 

 extension backwards of some of the sclerites, and their becoming 

 confounded with parts of the wall of the head. From all this it 

 appears that at present we cannot correctly go farther than 

 saying that the trophi of Hemiptera are the appendages of three 

 head-segments, like those of other Insects. The views of Savigny, 

 Leon, 3 and others to the effect that labial palpi, and even other 

 parts of the labium of Mandibulata can be satisfactorily identified 

 are not confirmed by Heymons. 



Underneath the pharynx, in the head, there is a peculiar 

 structure for which we have as yet no English term. It was 

 apparently discovered by Landois and Paul Mayer, 4 and has been 

 called " Wanzenspritze," which we translate as syringe. It may be 

 briefly described as a chamber, into which the salivary ducts open, 

 prolonged in front to the neighbourhood of the grooves of the 

 setae in the rostrum ; behind, it is connected with muscles ; 

 it has no direct connection with the pharynx, and though it was 

 formerly supposed to be an organ of suction, it seems more prob- 

 able that it is of the nature of a force-pump, to propel the pro- 

 ducts of some of the bug's glands towards the tips of the setae. 



The rostrum being extended from its position of repose, the 

 tip of the sheath is brought into contact with the object to be 

 pierced, the surface of which is probably examined by means of 

 sensitive hairs at the extremity of the sheath ; these therefore 

 functionally replace to some extent the palpi of other Insects. 

 As a rule the sheath does not penetrate (though there is reason 

 for believing that in various of the animal-feeding bugs it does 

 so), but the setae are brought into action for piercing the skin 

 of the plant ; they are extremely sharp, and the outer pair are 

 usually barbed, so that when once introduced a hold is easily 

 maintained. This being established it is thought that the salivary 

 pump comes into play, and that a fluid is injected into the object 

 pierced so as to give rise to irritation or congestion, and thus 

 keep up a supply of fluid at the point operated on : this fluid 

 extends along the grooved setae by capillary attraction, and the 



1 P. ent. soc. Washington, iii. 1895, p. 241. - Eut. Nachr. xxii. 1896, p. 173. 



3 Zool. Anz. 1897, No. 527, p. 73. 

 4 Arch. Anat. Physiol. 1874, p. 313, and 1875, p. 309. 



