COMPOSITION OF THE MOUTH IN INSECTS. 313 



to the imbibition of fluid nutriment, and consequently constructed upon 

 very opposite principles ; yet, notwithstanding the apparent want of 

 resemblance, it has been satisfactorily demonstrated by Savigny* that 

 the parts composing a suctorial mouth are fundamentally the same as 

 those met with in the mouths of mandibulate insects, but transformed 

 in such a manner as to form a totally different apparatus. 



(824.) According to the distinguished authors of the < Introduction 

 to Entomology t/ there are five kinds of imperfect mouth adapted to 

 suction, each of which will require a separate notice. 



(825.) The first is met with among the Hemiptera, and is formed to 

 perforate the stalks and buds of vegetables, in order to procure the juices 

 which they contain ; or, in some bugs, it is employed to puncture the 

 integument of living animals for a similar purpose. This kind of mouth 

 is exhibited in fig. 156. First, there is a long jointed sheath (d), which 

 is in fact the lower lip (labium) considerably 

 elongated, and composed of three or four parts 

 articulated together ; secondly there is a small 

 conical scale covering the base of the sheath 

 last mentioned, and representing the upper lip ; 

 and between these are four slender and rigid 

 bristles or lancets (scalpetta) (c), that, when not 

 in use, are lodged in a groove upon the upper 

 surface of the sheath, so as to be concealed 

 from view. These lancets are, in reality, 

 only the mandibles and maxillae strangely 

 altered in their form and excessively length- Mouth of Notonecta . 

 ened, so as not merely to become efficient 



piercing instruments, but so disposed as to form by their union a suc- 

 torial tube, through which animal or vegetable fluids may be imbibed. 

 This kind of mouth, when not employed, is usually laid under the thorax, 

 between the legs, in which position it is easily seen in most Hemiptera. 

 In some families, as, for example, in the Plant-lice {Aphides}, it is of 

 extraordinary length : thus, in the aphis of the oak it is three times as 

 long as the whole body of the insect, projecting posteriorly like a tail ; 

 and in the fir-aphis it is still longer. 



(826). The second kind of mouth is that met with among the Diptera ; 

 and from its construction in some tribes, we may well understand how 

 they are enabled to become so seriously annoying. The Gnat and the 

 Mosquito furnish sufficiently well-known examples of the formidable 

 apparatus in question, which in the Horse-fly (Tabanus) seems to at- 

 tain its maximum of development. The oral organs of the Diptera are 

 composed of a sheath or proboscis, that represents the lower lip of the 

 mandibulate insects : it is sometimes coriaceous or horny in its texture ; 



* Memoires sur les Animaux saris Vertebres. 8vo. Paris, 1816. 

 t Kirby and Spence, vol. iii. p. 463. 



