INSECTS AFFECTIXG PARK AND WOODLAXD TREES 9 



The head of the insect bears the principal sense organs — the eyes and 

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

 These latter consist of the mandibles, the niaxillae with their palpi, and 

 the lower lip or lai)ium, which is also pro\ided with a pair of palpi. The 

 thorax bears the princi[jal organs of locomotion : the wings and the legs. 

 The former ma\" lie absent in some cases, as in the lowest order, the Th)'sa- 

 nura, in certain sexes and in some species of the high(;r orders. The hind 

 wings may be retluced to men; vestiges known as halteres or balancers, 

 as in the tlies. The wings may be covered 1)\' protective shields, the 

 elytra of beetles, or parth' thickenetl, like tht; anterior wings of the 

 Heteroptera, and to a still less extent of certain ( )rtlioptera. The modifi- 

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

 vestiture or absence thereof, relati\"e 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, femiu', tibia and tarsus. The hrst is the small segment close to the 

 body, the fenuir and tiliia are usually of nearl\- etjual 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 Ijearing 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 im[)ortant 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 difierences 

 occur between sijecies. 



