Class 3. Insecta. 



23S 



ttere is a grooved or tuberculate grinding denticle^ the latter being- 

 best developed in the herbivorous forms^ whilst the former is more 

 prominent in predaceous Insects. The first m. axilla usually con- 

 sists of six to eight joints, of which the basal joint (cardo) is short, the 

 second {stipes) large, and produced into two long lobes, the inner 

 [galea) being usually fringed with stifE setae along its outer edge ; the 

 outer (lacinia), in several forms, consisting of two joints. Sometimes 

 only a single lobe is present. The rest of the maxilla, which 

 usually consists of four to six joints, forms a curved palp. The first 

 maxillae are prehensile and gustatory in function, whilst the mandibles 

 are' masticatory ; sometimes, however, the former also assist in masti- 

 cation. The second maxillae are similar to the first, but are 

 distinguished by the fact that the two cardines are always fused to 

 form a single plate [mentum) ; the stipes, too, are more or less 

 completely fused, and the lobes are often considerably modified as 

 compared with those of the first maxillae ; the palps are like those of 

 the first maxillae, but never consist of more than four joints. The 

 second maxillae are usually spoken of as the labium, their palps 

 as the labial palps, the lobes as glonscB and paraglossce. The 

 labium is, of course, not comparable with the lower lip of the 

 Crustacea; it is, like the mandible and first maxillag, a pair of limbs, 

 and corresponds with the second maxillae of the Crustacea, whilst 

 the lower lip of the latter is a membranous fold which is not repre- 

 sented in the Insects. The labium here forms the posterior, as the 

 1 a b r u m forms the anterior, boundary of the mouth. 



In Insects with sucking mouth-parts the same elements 

 occur, but modified in different ways in accordance with the change 

 of function. In the Lepidoptera, the labrum is simply a short. 



Fig. 196. Diagrammatic transverse section of the proboscis of; A Butterfly, 

 B Ehynohota, C Tabanas (Gtad-fiy), D Musca (another of the Diptera in which 

 mandibles and first maxillae are wanting) . sw sucking tube through which the fluid passes 

 to the month ; s salivary tube, o labrum, m mandibles, Ic first maxillse, u labium, h hypo- 

 pharynx. — Orig. 



broad plate with no special significance ; the mandibles are rudi- 

 mentary or absent. The first maxillae on the other hand are 

 well-developed ; each possesses only a single lobe, which is elongate 

 and gutter-like, forming, with its fellow of the other side, a long 

 tube, open at the end ; this tube is the sucking apparatus, the 



