The entomologist's text book : an introduction to the natural history, structure, physiology and classification of insects, including the Crustacea and Arachnida . here the mesothorax almost occupies the entire thorax. Inthe Hymenoptera (fig. 124), the second pair of wings exist,but of a smaller size than the fore pan*; the metathorax isaccordingly more developed than in the Diptera, but issmaller than the mesothorax. If we now look at those orderswhich have the second pair of wings enlarged, we find themesothorax diminished, and the metathorax increased in sizeto a corresponding extent; this
The entomologist's text book : an introduction to the natural history, structure, physiology and classification of insects, including the Crustacea and Arachnida . here the mesothorax almost occupies the entire thorax. Inthe Hymenoptera (fig. 124), the second pair of wings exist,but of a smaller size than the fore pan*; the metathorax isaccordingly more developed than in the Diptera, but issmaller than the mesothorax. If we now look at those orderswhich have the second pair of wings enlarged, we find themesothorax diminished, and the metathorax increased in sizeto a corresponding extent; this is the case in the beetles, butmore especially in the extraordinary parasitic order, Strepsiptera, respecting which so much incorrect matter has beenpublished. The four pieces of which the upper side of each thoracic A A 3 270 PTILOTA : IMAGO—EXTERNAL ANATOMY. segment is typically composed, are sufficiently distinct in themesonotum; the first, or the prsescutum (« 2) (prophragma,Kirby and Spence); and the second, b 2, scutum (or thedorsulum, Kirby and Spence), are both distinct,but not conspi-cuous parts in the Coleoptera, in which order the third 126 Figs. 126, dorsal view of the thorax of a Tabanus ; ll!7, lateral view of ditto, lettered asin fig-s. llS-123. (c 2), is very conspicuous, being the triangular part which isfound at the base of the elytra, where they vmite together,and is ordinarily termed the scutellum; but more properlythe scutellum of the mesothorax or mesoscutellum. Somebeetles, indeed, are said to be exscutellated, or destitute ofscutellum; and so far as its occupying the ordinary exposedsituation is concerned, they are exscutellated; but the samepart is to be found in a diminished form in all these beetles. In some few insects, as the ScutellercB {TetyrcB), the scutel-lum is so much enlarged, that it completely covers the abdo-men. The postscutellum of the mesothorax, {d 2) or thefrcenum of Kirby and Spence, is also distinct, but not veryconspicuo
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Keywords: ., bookau, bookcentury1800, booksubjectcrustacea, booksubjectinsects
