But in June it has lost this withered appearance; it represents a perfect balloon, an ellipsoid of which the sections perpendicular to the major axis are circles. Something has also come to pass of greater importance than this expansion, which may be compared with that which we obtain by blowing into a wrinkled bladder. The horny integuments of the pseudochrysalis have become detached from their contents, all of a piece, without a break, just as happened the year before with the skin of the secondary larva; and they thus form a fresh vesicular envelope, free from any adhesion to the contents and itself enclosed in the pouch formed of the secondary larva's skin. Of these two bags without outlet, one of which is enclosed within the other, the outer is transparent, flexible, colourless and extremely delicate; the second is brittle, almost as delicate as the first, but much less translucent because of its yellow colouring, which makes it resemble a thin flake of amber. On this second sac are found the stigmatic warts, the thoracic studs and so forth, which we noted on the pseudochrysalis. Lastly, within its cavity we catch a glimpse of something the shape of which at once recalls to mind the secondary larva.
And indeed, if we tear the double envelope which protects this mystery, we recognize, not without astonishment, that we have before our eyes a new larva similar to the secondary. After one of the strangest transformations, the creature has gone back to its second form. To describe the new larva is unnecessary, for it differs from the former in only a few slight details. In both there is the same head, with its various appendages barely outlined; the same vestiges of legs, the same stumps transparent as crystal. The tertiary larva differs from the secondary only by its abdomen, which is less fat, owing to the absolute emptiness of the digestive apparatus; by a double chain of fleshy cushions extending along each side; by the rim of the stigmata, crystalline and slightly projecting, but less so than in the pseudochrysalis; by the ninth pair of breathing-holes, hitherto rudimentary but now almost as large as the rest; lastly by the mandibles ending in a very sharp point. Evicted from its twofold sheath, the tertiary larva makes only very lazy movements of contraction and dilation, without being able to advance, without even being able to maintain its normal position, because of the weakness of its legs. It usually remains motionless, lying on its side, or else displays its drowsy activity merely by feeble, wormlike movements.
By dint of these alternate contractions and dilations, indolent though they be, the larva nevertheless contrives to turn right round in the sort of shell with which the pseudochrysalidal integuments provide it, when by accident it finds itself placed head downwards; and this operation is all the more difficult inasmuch as the larva almost exactly fills the cavity of the shell. The creature contracts, bends its head under its belly and slides its front half over its hinder half by wormlike movements so slow that the lens can hardly detect them. In less than a quarter of an hour the larva, at first turned upside down, finds itself again head uppermost. I admire this gymnastic feat, but have some difficulty in understanding it, so small is the space which the larva, when at rest in its cell, leaves unoccupied, compared with that which we should be justified in expecting from the possibility of such a reversal. The larva does not long enjoy the privilege which enables it to resume inside its cell, when this is moved from its original position, the attitude which it prefers, that is to say, with its head up.
Two days, at most, after its first appearance it relapses into an inertia as complete as that of the pseudochrysalis. On removing it from its amber shell, we see that its faculty of contracting or dilating at will is so completely paralysed that the stimulus of a needle is unable to provoke it, though the integuments have retained all their flexibility and though no perceptible change has occurred in the organization. The irritability, therefore, which in the pseudochrysalis is suspended for a whole year, reawakens for a moment, to relapse instantly into the deepest torpor. This torpor will be partly dispelled only at the moment of the passing into the nymphal stage, to return immediately afterwards and last until the insect attains the perfect state.
Further, on holding larvæ of the third form, or nymphs enclosed in their cells, in an inverted position, in glass tubes, we never see them regain an erect position, however long we continue the experiment. The perfect insect itself, during the time that it is enclosed in the shell, cannot regain it, for lack of the requisite flexibility. This total absence of movement in the tertiary larva, when a few days old, and also in the nymph, together with the smallness of the space left free in the shell, would necessarily lead to the conviction, if we had not witnessed the first moments of the tertiary larva, that it is absolutely impossible for the creature to turn right round.
And now see to what curious inferences this lack of observations made at the due moment may lead us. We collect some pseudochrysalids and heap them in a glass jar in all possible positions. The favourable season arrives; and with very legitimate astonishment we find that, in a large number of shells, the larva or nymph occupies an inverted position, that is to say, the head is turned towards the anal extremity of the shell. In vain we watch these reversed bodies for any indications of movement; in vain we place the shells in every imaginable position, to see if the creature will turn round; in vain, once more, we ask ourselves where the free space is which this turning would demand. The illusion is complete: I have been taken in by it myself; and for two years I indulged in the wildest conjectures to account for this lack of correspondence between the shell and its contents, to explain, in short, a fact which is inexplicable once the propitious moment has passed.
On the natural site, in the cells of the Anthophora, this apparent anomaly never occurs, because the secondary larva, when on the point of transformation into the pseudochrysalis, is always careful to place its head uppermost, according as the axis of the cell more or less nearly approaches the vertical. But, when the pseudochrysalids are placed higgledy-piggledy in a box or jar, all those which are upside down will later contain inverted larvæ or nymphs.
After four changes of form so profound as those which I have described, one might reasonably expect to find some modifications of the internal organization. Nevertheless, nothing is changed; the nervous system is the same in the tertiary larva as in the earlier phases; the reproductive organs do not yet show; and there is no need to mention the digestive apparatus, which remains invariable even in the perfect insect.
The duration of the tertiary larva is a bare four or five weeks, which is also about the duration of the second. In July, when the secondary larva passes into the pseudochrysalid stage, the tertiary larva passes into the nymphal stage, still inside the double vesicular envelope. Its skin splits along the back in front; and with the assistance of a few feeble contractions, which reappear at this juncture, it is thrust behind in the shape of a little ball. There is therefore nothing here that differs from what happens in the other Beetles.
Nor does the nymph which succeeds this tertiary larva present any peculiarity: it is the perfect insect in swaddling-bands, yellowish white, with its various external members, clear as crystal, displayed under the abdomen. A few weeks elapse, during which the nymph partly dons the livery of the adult state; and, in about a month, the insect moults for a last time, in the usual manner, in order to attain its final form. The wing-cases are now of a uniform yellowish white, as are the wings, the abdomen and the greater part of the legs; very nearly all the rest of the body is of a glossy black. In the space of twenty-four hours, the wing-cases assume their half-black, half-russet colouring; the wings grow darker; and the legs finish turning black. This done, the adult organism is completed. However, the Sitaris remains still a fortnight in the intact shell, ejecting at intervals white droppings of uric acid, which it pushes back together with the shreds of its last two sloughs, those of the tertiary larva and of the nymph. Lastly, about the middle of August, it tears the double bag that contains it, pierces the lid of the Anthophora's cell, enters a corridor and appears outside in quest of the other sex.