EXTERNAL ANATOMY OF INSECTS. 405 



vertically, we should then have an upper Up, a pair of upper 

 jaws, a tongue, a pair of lower jaws, and an under Up, or, in 

 entomological language, a lahrum, two mandibulce, a Ungua, 

 two maxiUcE, and a labium, which parts are always present in 

 the principal forms of every class, and in no insect yet disco- 

 vered has any new or additional primary part been detected ; 

 nevertheless, there are epiphysal appendages, or secondary 

 parts, called palpi, these are four or six in number,'' and are 

 articulated on the maxillce and labium. The variations in the 

 form of these constituent parts of the mouth have been used by 

 Fabricius as the exclusive characters on which to found his 

 classes, and perhaps are more sound and unobjectionable than 

 any others taken singly. 



In the first class, JLepidoptera, the labrum is scarcely dis- 

 tinguishable, the labium is distinct but short ; it gives rise to 

 two large, conspicuous, erect, orporrected jy«/^i, between which 

 are situated the maxillcs, v/hich are in this class two long 

 tubes, rolled up spirally when at rest, in the manner of 

 the main-spring of a watch, but capable of being unrolled 

 at will for the purpose of being inserted into the corollce of 

 flowers to extract their honey : the lingua and mandibulce 

 are nearly obsolete, and take no part in the functions of 

 manducation. This mouth is termed antliate by Kirby. In 

 the second class, Diptera, the labrum and labium combine 

 in forming a stiff hollow cylinder, in which are contained the 

 mandibulce, maxillce, and lingua ; these are excessively sharp- 

 pointed, and are thrust by the animal into substances (as leaves, 

 fruit, flesh, &;c.) for the purpose of making an incision, through 

 which the fluid portion (as sap, juice, blood, &c.) may flow 

 into the cylinder, formed by the united lips, which, by the 

 creation of a vacuum on the plan of a syphon, conveys the juice 

 through the oesophagus into the stomach. This mouth is 

 termed proboscidate by Kirby. In the third class, Hymenop- 

 tera, the labrum, mandibulce, maxillce, lingua, and labium, 

 are all fully developed ; the office and appearance of the 

 77iandibulcB and maxillce are now changed, acting neither as 

 suckers nor lancets, but being hard, strong, horny jaws, emi- 

 nently adapted to gnawing and detrition of hard and solid 

 substances, of which office, in the preceding classes, they are 



'"■ Epiphysal parts vary in number, constituent primary parts never. 



