MOUTHPARTS OF INSECTS 325 



furnished with a distinct head, followed by a considerable num- 

 ber of similar segments, each bearing one or two pairs of legs. 

 There is a single pair of antennae. Although some of the centi- 

 pedes are poisonous, none of the myriapods are parasitic, nor 

 are any of them known to be disease carriers. 



The Insecta, or insects, represent the zenith of invertebrate 

 life. They are terrestrial arthropods which, like the myriapods, 

 breathe by tracheae. Their appendages, however, are reduced 

 to one pair of antennae, two pairs of mouthparts and three pairs 

 of legs with usually the addition, if not secondarily lost, of two 

 pairs of wings. The wings are really mere outgrowths or folds 

 of the integument or " skin " of the insect, between the two layers 

 of which are branches of the tracheae, represented by the " veins" 

 in the wings of adult insects. There is a fundamental plan of ar- 

 rangement of the veins which is variously modified in different in- 

 sects, but absolutely fixed in any given species. The venation 

 of the wings is often of great value in the identification of genera 

 or species of insects. An insect is always readily divisible into 

 three parts, the head, thorax and abdomen. The head, in addi- 

 tion to the antennae already mentioned, bears two compound eyes 

 sometimes of relatively enormous size, usually several simple eyes, 

 and the mouthparts. 



Mouthparts of Insects. Incredible as it may seem at first 

 thought, the mouthparts of all kinds of insects, from the simple 

 chewing organs of a grasshopper to the highy modified piercing 

 and sucking organs of biting flies and mosquitoes and the great 

 coiled sucking tube of butterflies and moths, are modifications 

 of a single fundamental type. This type is represented in its 

 simplest form in the chewing or biting type, as found in grass- 

 hoppers and beetles (Fig. 134). The mouthparts in these in- 

 sects consist (1) of an upper lip or labrum (Fig. 134, Lbr.); 

 (2) a lower lip or labium (Fig. 134, Lbm.), really formed of a 

 pair of organs fused together, each bearing a segmented appen- 

 dage, the labial palpus (Fig. 134, Lab. p.); (3) a pair of hard, 

 horny, toothed mandibles or jaws (Fig. 134, Mand.) lying just 

 under the lower lip, which chew up food by a horizontal instead 

 of vertical movement; (4) a pair of maxillae (Fig. 134, Max.), 

 lying between the mandibles and lower lip, each bearing a seg- 

 mented appendage more or less like those on the lower lip, and 

 called the maxillary palpus (Fig. 134, Max. p.) and (5) the 



