IXSlA IS AKKECTING I'AKK AXU W OUULAND TRliliS 9 



The head of the insect hears tht; principal sense organs — the eyes and 

 the antennae — and also those for tht; prehension and mastication of food. 

 These latter consist ol the mandibles, the maxilhu! with their indpi, and 

 the lower lip or labium, w hich is also proxitled with a i)air of palpi. The 

 thora.x bears the principal orj^ans of locomotion : the winys and the legs. 

 The former may be absent in some cases, as in tin- lowi'st order, the Thysa- 

 nura, in certain sexes and in some species of tht- higher orders. The hind 

 wings may be reduced to mere vestiges know n as halteres or balancers, 

 as in the Hies. The wings ma)' be covered b\- protective shields, the 

 elytra of beetles, or partly thickened, like the anterior wings of the 

 Heteroptera, and to a still less extent of certain Orthoptera. The modifi- 

 cations existing in these organs are of great aid in classification. The 

 vestiture pr absence thereof, relative length, number of veins, location of 

 veins, arrangement of cells and other differences are of great service to the 

 systematist. 



The legs are normally six in number, though occasionally there are 

 species which have but four, the anterior two in some butterflies being 

 reduced to mere rudiments. The principal parts of the leg are the trochan- 

 ter, femur, tibia and tarsus. The first is the small segment close to the 

 body, the femur and tibia are usually of nearly equal length, the femur 

 being decidedly stouter, while the tarsus is rather slender and usually con- 

 sist of from three to five segments, the terminal one bearing a pair of claws 

 or a sucking disk or both. There are considerable modifications in 

 each of these parts, and their relative development, length, clothing, 

 color etc. afford good characters for the separation of important groups 

 and species. 



The abdomen has lo or fewer segments and is usually considerably 

 longer than the harder, more complex thorax. It is composed of a series 

 of very similar segments, the terminal ones bearing the sexual organs, which 

 are very diverse in different orders, families, and sometimes great differences 

 occur between species. 



