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By consulting only the bones, the vertebrae, the hair, the nervures of the wings, the joints of the antennae, the imagination may build up any sort of genealogical tree that will fit with our theories of classification, for, when all is said, the animal, in its widest generalization, is represented by a digestive tube. With this common factor, the way lies open to every kind of error.
From the rubbing of the belly against the network of nervures proceeds the species of puffing sound which I have compared to the hissing of an adder in a posture of defence. To imitate this curious sound it is enough rapidly to stroke the upper face of an outstretched wing with the tip of the finger-nail.
In our British Phasgonura viridissima it appeared to me that the serrated nervure is rubbed against the rounded hind-corner of the opposite wing, the edge of which is thickened, coloured brown, and very sharp. In the right wing, but not in the left, there is a little plate, as transparent as talc, surrounded by nervures, and called the speculum.
As a general rule, insect wings that are intended for employment in flight are transparent membranes, with the course of the air-tubes marked out upon them as opaque nervures. These air-tubes, it will be remembered, are lined by spires of dense cartilage; and hence it is that they become nervures so well adapted to act like tent-lines in keeping the expanded membranes stretched.
He says, "It is remarkable for having a sort of drum at the base of the fore wings, between the costal nervure and the subcostal. These two nervures, moreover, have a peculiar screw-like diaphragm or vessel in the interior." Catherine's on the coast of Brazil, a butterfly called Februa Hoffmanseggi, makes a noise, when flying away, like a rattle.
Then the thorax splits along the back, and through the fissure the insect slowly emerges. The whole process lasts perhaps half an hour. There is the adult insect, freed of its mask, and how different from what it was but how! The wings are heavy, moist, transparent, with nervures of a tender green. The thorax is barely clouded with brown.
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.
I see other nervures in the intervals, pale and very fine. Finally, still more delicate, and running transversely, a number of very short nervures complete the pattern. Certainly this resembles a rough sketch of the future wing-case; but how different from the mature structure!
We may dissect, we may scrutinize organs under the magnifying glass, examine wing-cases, count the nervures of the wings, the number of articulations in the limbs; we may reckon every point, like Réaumur forgetting not a line, not a hair; we may compare and measure every portion of the mouth, and define the class; and we shall not find a single point in all this physical architecture which will positively inform us of the habits of the insect.
The insect has an inflated bladder-like shape, owing to the great convexity of the thin, firm, parchmenty wing-cases; the little creature being of a pale green colour. The instrument by which it produces its music is contrived out of the ordinary nervures of the wing-case. In each wing-case the under edge of the wing itself has a horny lobe.
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