MOUTH -PARTS 345 



is formed of the interlocked galese of the maxillae, and is carried 

 at rest coiled up under the head. All the other parts are reduced 

 or absent except for a three-jointed labial palp (Fig. 178). 



The bees have peculiar mouth-parts best known as licking and 

 sucking (Fig. 179) ; they collect pollen as well as feeding on 

 nectar, and also use their mouth-parts for building. The proboscis 

 is formed by the elongated and fused glossae of the labium, and 

 food is sucked up a groove on the dorsal surface of this. The well- 

 developed labial palp and galeae surround the glossa and probably 

 help to form the tube. The mandibles are used for building. 



WINGS 



Although insects are typically flying creatures, wings are 

 absent from the most primitive living orders, and have also been 

 lost by a number of other groups, particularly parasites such as 

 fleas, lice, and bed bugs, but also by some free-living forms. 

 The simplest condition is for both pairs of wings to be functional, 

 membranous, and alike. When both pairs are used they are 

 often locked together, so that they beat as one ; the bees have 

 a series of hooks, and the butterflies have interlocking bristles. 

 The beetles have the front pair of wings modified, even more 

 strongly than in the cockroach, to form hard wing-cases, known 

 as elytra or shards. In the butterflies and moths both pairs are 

 covered with small scales, which also clothe the rest of the body, 

 and come off as a powder when the insect is handled. The flies 

 in the strict sense (Diptera, p. 256) have lost the hind pair, 

 which are represented only by small knobs, the halteres (sing., 

 halter) or balancers, which assist in maintaining the animal's 

 balance in flight. 



LIFE-HISTORIES 



The different orders of insects have various types of life- 

 history, according to their habitat and evolutionary level, but 

 it is very common for there to be a larva, by which should be 

 meant an immature form, living a life independent of the parents, 

 and possessing structures which are not present in the adult. Since 

 insects are arthropods they undergo the characteristic moults or 

 ecdyses which are necessary to allow the inelastic cuticle to be 

 replaced. The period between two ecdyses is a stadium, and the 

 form of a larva in a particular stadium is an instar. The last instar 

 which comes after the last ecdysis, is the adult or imago (pi.. 



