a guide to the study of british waterbugs. 5 



The Eostrum. 



Although greatly modified, all the principal parts of the 

 mouth, present in the Mandibulate Hexapoda, can be traced in 

 the Khynchota. 



The upper lip [Labrum) is usually very short and more or 

 less triangular in form, covering the base of the labium. The 

 lower lip (Labium, Second Maxilla, &c.) forms an elongate, 

 subcylindric tube (consisting normally of four segments) which 

 acts as a kind of suction-pump for the conveyance of nourish- 

 ment to the digestive apparatus; it also serves as a sheath and 

 support for the four sharp, thread-like setae which represent the 

 first maxillae [interior seta) and the mandibles [exterior seta). 

 These parts are apparently always present, but their appendages 

 are very obscure, and specialists are by no means agreed on the 

 subject.* 



The general impression as to the method of feeding employed 

 by Khynchota appears to be that the "rostrum" (i.e. the labium) 

 is thrust into the food-substance — animal or vegetable --the sur- 

 face of which is penetrated by the thrust of the rostrum. On 

 examining the latter, however, we find that the apex is usually 

 blunt or slightly concave, clothed with hairs or bristles, and 

 quite incapable of piercing the epidermis of an insect or plant. 

 In reality, the desired surface is punctured by the long, acute, 

 often serrated, mandibular setae (which, as remarked previously, 

 are, at rest, concealed in the labium), and the apex of the 

 labium is then applied immediately (rarely pushed well in), and 

 the contents of the food-substance pumped up.f The blunter 

 and shorter maxillary setae apparently serve for the conduction 

 of saliva. 



The Antenna. 



Four segments appear to be the normal composition of the 

 antennae, though Hebrns possesses 5, with one or two interca- 

 lated nodes, and in Micronecta and the Nepidae there are apparently 

 only 3. In the Hebridae and Gerridae they are long, free, more 

 or less thread-shaped {filiform), the apical segment often swollen 

 and furnished with thick hairs. In Aphelocheirus they are sub- 

 cylindric, long and slender (the apical segment rather long), and, 



* For the latest papers, see Leon's " Beitriige zur Kenntn. der 

 Mundteile des Hemipteren," Jena, 1887 ; the same author's " LaHaltaster 

 bei Hernipt." (1892, ' Zool. Anzeig.' pp. 145-7), and " Beitriige zur Kenntn 

 des Labiums der Hydrocoren " (1897, ' Zool. Anz.' pp. 73-7) ; in the latter 

 the mouth-parts of Gerris najas and an extra-British species of Velia are 

 figured. See also a preliminary paper by Heymons, "Die Mundteile der 

 Ehynchota" (1896, * Entom. Nachr.' xxii. pp. 173-5). 



| I think the first author to call attention to this was Marlatt : see " The 

 Hemipterous Mouth" ('Trans. Ent. Soc. Wash.' hi. pp. 241-9); "How 

 Hemiptera Feed " (1895, ' Insect Life,' vii. pp. 427, 428) ; and " The Periodical 

 Cicada" (1898, ' Bull. U.S. Agric.,' new series 14, pp. 52, 53). 



