Fig. 4.—Digestive apparatus of the Sacred Beetle.
We must not finish the history of the grub without saying a few words on its internal structure. Anatomy will show us the works wherein the cement employed in so original a manner is manufactured. The stomach or chylific ventricle is a long, thick cylinder, starting from the creature’s neck after a very short gullet. It measures about three times the length of the animal. In its last quarter, it carries a voluminous lateral pouch distended by the food. This is a subsidiary stomach in which the supplies are stored so as to yield their nutritive principles more thoroughly. The chylific ventricle is much too long to lie straight in the grub’s bowels and bends back upon itself, in front of its appendix, in the form of a large loop occupying the dorsal surface. It is to contain this loop and the lateral pouch that the back is swollen into a protuberance. The grub’s wallet is, therefore, a second paunch, an annexe, as it were, of the stomach, which is itself incapable of holding the voluminous digestive apparatus. Four very fine, very long tubulures, irregularly entwined, four Malpighian vessels mark the limits of the chylific ventricle. [[48]]
Next comes the intestine, narrow, cylindrical, rising forwards. The intestine is followed by the rectum, which pushes backwards. This latter, which is of exceptional size and fitted with powerful walls, is wrinkled across, bloated and distended by its contents. Here is the roomy warehouse in which the scoriæ of the digestion accumulate; here is the mighty ejaculator, always ready to provide cement.
The grub gets bigger as it eats the wall of its house from the inside. Little by little, the belly of the pear is scooped out into a cell whose capacity grows in proportion to the growth of the inhabitant. Ensconced in its hermitage, furnished with board and lodging, the recluse waxes stout and fat. What more does it want?
In four or five weeks, the complete development is obtained. The apartment is ready. The worm sheds its skin and becomes a chrysalis. There are very few in the entomological world to vie in sober beauty with the tender creature which, with its wing-cases laid in front of it like a wide-creased scarf and its fore-legs folded under its head, as when the full-grown Scarab counterfeits death, suggests the idea of a mummy maintained by its bandages in a sacerdotal pose. Semi-translucent and honey-yellow, it looks as though it were cut from a block of amber. Imagine it hardened in this state, mineralized, made incorruptible: it would be a splendid topaz jewel.
In this marvel, so severe and dignified in shape and colouring, one point above all captivates me and gives me at last the solution of a far-reaching problem. Are the front-legs furnished with a tarsus, yes or no? This is the great business that makes me forget the jewel for the sake of a structural detail. Let us then return to a subject that excited me in my early days; for the answer [[49]]has come at last, late, it is true, but certain and indisputable.
By a very strange exception, the full-grown Sacred Beetle and his congeners are without front tarsi; they lack on their fore-legs that five-jointed finger which is the rule among the highest division of Coleoptera, the Pentamera. The other limbs, on the contrary, follow the common law and possess a very well-shaped tarsus. Is the formation of the toothed armlets original or accidental?
At first sight, an accident seems probable enough. The Scarab is a strenuous miner and a great pedestrian. Always in contact with the rough soil, whether in walking or digging; used, moreover, for constant leverage when the insect is rolling its ball backwards, the fore-legs are much more exposed than the others to the danger of spraining and twisting their delicate finger, of putting it out of joint, of losing it entirely, from the very first moment when the work begins.
Lest this explanation should appeal to any of my readers, I will hasten to undeceive them. The absence of the front fingers is not the result of an accident. The proof of what I say lies here, under my eyes, without the possibility of a rejoinder. I examine the nymph’s legs with the magnifying-glass: those in front have not the least vestige of a tarsus; the toothed limb ends bluntly, without a trace of a terminal appendage. In the others, on the contrary, the tarsus is as distinct as possible, notwithstanding the shapeless, gnarled condition due to the swaddling-bands and the humours of the chrysalis state. It suggests a finger swollen with chilblains.