INSECT A. 195 



of species of insects ; and a considerable section of the glossology of 

 this extensive department of Natural History is devoted to the 

 technical terms required to express the antennal characters. To the 

 head likewise belong more or less complicated oral instruments, 

 called " trophi," or "■ instrumenta cibaria," modified in some insect? 

 to serve for suction, in others, for mastication : they properly fall 

 under the demonstration of the digestive system. 



The jointed legs attached, as before stated, to the three thoracic 

 segments, consist each of a hip, a thigh (A), a leg (/), and a foot (w), 

 commonly called the tarsus ; but which are not to be taken as 

 rigorously answerable to the parts so termed in Human Anatomy. 

 The hip, for example, consists of two joints, usually the shortest of 

 the whole leg: the foot or tarsus includes from two to five joints, and 

 is terminated by a pair of diverging hooks or claws. The peculiar 

 powers of moving upon land or in water depend upon the modi- 

 fications of the forms or proportions of these extremities. In water 

 insects the tarsi are usually flattened, fringed with hair, and stretched 

 out in the same plane with the trunk, like oars. In leaping insects 

 the hinder limbs present as disproportionate a development as the 

 legs of the kangaroo. In burrowing insects, the anterior limbs are dis- 

 tinguished by short, broad, and massive proportions, with a strong and 

 flattened hand, like that of the mole, as in this best of insect burro wers *, 

 which has been called the mole-cricket. Most insects are able to 

 crawl up vertical walls, and some along glass and the ceilings of 

 rooms, against gravity : the house-fly achieves this by virtue of the 

 development of little suckers upon the under surface of certain ex- 

 panded joints of the tarsus. 



The wings of insects are essentially flattened vesicles, sustained by 

 slender but firm hollow tubes called " nervures," along which branches 

 of the tracheae, and channels of the circulation, are continued. The 

 wings never exceed two pairs, which are developed from the meso- 

 notum and metanotum. Sometimes one or other of these pairs is 

 wanting. The wings present many varieties in their shape, their 

 consistence, and their teguments. When they subserve flight, they 

 are thin and transparent ; or if opake, are rendered so by an im- 

 bricated clothing of most delicate scales, which, when detached, 

 resemble the pollen of flowers. In certain insects, especially those 

 that burrow, the first pair of wings become thick, hard, and opake, 

 forming a kind of shield to the back ; they are called " elytra," and 

 cover the posterior pair of membranous wings when these are not 

 expanded for flight. Sometimes the anterior wings are membranous 



* Prep. No. 463, A. 



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