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By what steps the more simple apparatus in the Achetidae originated, we do not know, but it is probable that the basal portions of the wing- covers originally overlapped each other as they do at present; and that the friction of the nervures produced a grating sound, as is now the case with the wing-covers of the females. Mr.
Bernadette alone struggled on to the finish, so pleased she was at being there, in that narrow nave whose slender nervures were coloured blue and red. At the farther end was the altar, also painted and gilded, with its twisted columns and its screens on which appeared the Virgin and Ste. Anne, and the beheading of St. John the Baptist the whole of a gaudy and somewhat barbaric splendour.
The three rose windows in the semicircular apse are richly decorated with ogival nervures, and correspond, one to the nave and one to each of the aisles; they belong to the primitive structure, having illuminated the afore-mentioned chapels.
Let us suppose that this convex scale is pulled out of shape from the interior, so that it is slightly flattened and as quickly released; it will immediately regain its original convexity owing to the elasticity of the nervures. From this oscillation a ticking sound will result. Twenty years ago all Paris was buying a silly toy, called, I think, the cricket or cri-cri.
The disposition of the radiating nervures, the skeleton of the structure, is not at all the same; the network formed by the cross-nervures gives no idea whatever of the complex final arrangement. The rudimentary is succeeded by the infinitely complex; the clumsy by the infinitely perfect, and the same is true of the sheath of the wing and the final condition of its contents, the perfect wing.
The powerful nervures of the dorsal portion of the wing-cover are of the deepest black, and their general effect is that of a complicated design, not unlike a tangle of Arabic caligraphy.
These tongues may be compared to the blade of a watchman's rattle, only instead of engaging with the teeth of a rotating wheel they touch the nervures of the vibrating cymbal. From this fact, I imagine, results the harsh, grating quality of the cry. It is hardly possible to verify the fact by holding the insect in the fingers; the terrified Cacan does not go on singing his usual song.
The total length of the body is two inches and a quarter; when the wings are closed the insect has an inflated vesicular or bladder-like shape, owing to the great convexity of the thin but firm parchmenty wing-cases, and the colour is wholly pale-green. The instrument by which the Tanana produces its music is curiously contrived out of the ordinary nervures of the wing-cases.
Hence we may infer with confidence that the Locustidae are descended from a form, in which, as in the existing Achetidae, both wing-covers had serrated nervures on the under surface, and could be indifferently used as the bow; but that in the Locustidae the two wing-covers gradually became differentiated and perfected, on the principle of the division of labour, the one to act exclusively as the bow, and the other as the fiddle.
This last nervure, which is of a slightly reddish hue, is the fundamental element of the musical device; it is, in short, the bow, the fiddlestick, as is proved by the fine notches which run across it. The rest of the wing-cover shows a few more nervures of less importance, which hold the membrane stretched tight, but do not form part of the friction apparatus.
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