The entomologist's text book : an introduction to the natural history, structure, physiology and classification of insects, including the Crustacea and Arachnida . He Ukewise considers them as somewhatanalogous to the lateral prolongation of the prothorax, ob-served in some species of Psychodce and Scenopinus (dipte-rous genera). As already observed, however, they have beendemonstrated to be the only mesothoracic appendages foundto exist in these insects (the wings being metathoracic); con-sequently they must be regarded as analogues of the meso-thoracic organs of flight. During the short time
The entomologist's text book : an introduction to the natural history, structure, physiology and classification of insects, including the Crustacea and Arachnida . He Ukewise considers them as somewhatanalogous to the lateral prolongation of the prothorax, ob-served in some species of Psychodce and Scenopinus (dipte-rous genera). As already observed, however, they have beendemonstrated to be the only mesothoracic appendages foundto exist in these insects (the wings being metathoracic); con-sequently they must be regarded as analogues of the meso-thoracic organs of flight. During the short time that theseinsects live in the winged state, the pseudhalteres are ob-served to quiver very intensely. 2. Ler/s, or the Organs of terrestrial or aquatic Progres-sion.—If we have found the organs of flight constructed in amanner totally unlike those of birds, we shall discover equal-ly great diff*erences in the construction of their legs. Thus,whilst the former are provided T\ith but a pair of organs forprogression on the land, winged insects have three pairs, spi-ders four pairs, crabs five pairs, and centipedes and millipedes more than a hundred J39 136. These organs legs. arise from the ster-num fof the [varioussegments of the tho-rax in the true insects,and are employed notonly in walking, run-ning, creeping, andclimbing, but also inrunning and swim-ming, as well as invarious operations con-nected with their eco-nomy. They consistof a series of tubular joints, formed of a similar substancewith the remainder of the external parts of the body, and J41 LEGS. 287 are provided with internal muscles and nerves. Thejoints have received a series of names analogous tothose of the legs of the higher animals. They are the coxa,trochanter, femur, tibia, and tarsus. The coxa (136, a) is thebasal joint articulating with the sternum, and very variablein form. The trochanter (136, li) is a very small piece con-necting the preceding Avith the thigh or femur (136, c),which in general is the
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Keywords: ., bookau, bookcentury1800, booksubjectcrustacea, booksubjectinsects
