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Show 56 ON CLASSIFICATION. posed essentially as in this and the two preceding classes. But the total number of somites of the body never exceeds twenty. Fig. 28. Fig. ~~1. Fig. 29.-Longitudinal and vertical section of the abdomen of a male Cockroach (Blatta ).-1, 2, 3, 4, &c., terga and stema of the abdomen ; t, testis ; v~ aperture of the vas deferens ; A, anus. THE INSEC'l'A. 57 Of the o five certainly, and six probabl.v, con titute tho head, which possesses a pair of antenn(. , a pair of n1andible,, and two pairs of 1naxillce ; the hinder pair of which arc eoal scent, and fonn the organ called the "labium." 'rhree, or perhaps, )n some cases, Inore, son1ites unite nncl become specially modifieJ to fonn the thorax, to which th' three pairs of locomotive limbs, cbaracteri tic of perfect in ct ·, * are attached. Two additional pairs of locomotive organs -the wing - are developed, in 1nost insects, from the tergal walls of the second and third thoracie somites. No locomotive limbs are ever developed from the abdomen of the adult insect, but th ventral portions of the abdmninal son1ites, from tho eighth backwards, are often metmnorphosed into apparatuses an illary to the generative function (Figs. 28 and 29). * Tllo female Stylops is stateu to possess no thoracic limbs. |
