第23章 THE CETONIA-LARVA(4)

>From it run numbers of filaments which actuate the feet and the powerful muscular layer which is the creature's essential motor organ. When examined merely through the pocket-lens, this cylinder appears to be slightly furrowed transversely, a proof of its complex structure. Under the microscope, it is seen to be formed by the close juxtaposition, the welding, end to end, of the ganglia, which can be distinguished one from the other by a slight intermediate groove. The bulkiest are the first, the fourth and the tenth, or last; these are all very nearly of equal size. The rest are barely half or even a third as large as those mentioned.

The Interrupted Scolia experiences the same hunting and surgical difficulties when she attacks, in the crumbling, sandy soil, the larvae of the Shaggy Anoxia or of the Morning Anoxia, according to the district; and these difficulties, if they are to be overcome, demand in the victim a concentrated nervous system, like the Cetonia's. Such is my logical conviction before making my examination; such also is the result of direct observation. When subjected to the scalpel, the larva of the Morning Anoxia shows me its centres of innervation for the thorax and the abdomen, gathered into a short cylinder, which, placed very far forward, almost immediately after the head, does not run back beyond the level of the second pair of legs. The vulnerable point is thus easily accessible to the sting, despite the creature's posture of defence, in which it contracts and coils up. In this cylinder I recognize eleven ganglia, one more than in the Cetonia. The first three, or thoracic, ganglia are plainly distinguishable from one another, although they are set very close together; the rest are all in contact. The largest are the three thoracic ganglia and the eleventh.

After ascertaining these facts, I remembered Swammerdam's investigations into the grub of the Monoceros, our Oryctes nasicornis. (Jan Swammerdam (1637-1680), the Dutch naturalist and anatomist.--Translator's Note.) Ichanced to possess an abridgement of the "Biblia naturae," the masterly work of the father of insect anatomy. I consulted the venerable volume. It informed me that the learned Dutchman had been struck, long before I was, by an anatomical peculiarity similar to that which the larvae of the Cetoniae and Anoxiae had shown me in their nerve-centres. Having observed in the Silk-worm a nervous system formed of ganglia distinct one from the other, he was quite surprised to find that, in the grub of the Oryctes, the same system was concentrated into a short chain of ganglia in juxtaposition. His was the surprise of the anatomist who, studying the organ qua organ, sees for the first time an unusual conformation. Mine was of a different nature: I was amazed to see the precision with which the paralysis of the victim sacrificed by the Scolia, a paralysis so profound in spite of the difficulties of an underground operation, had guided my forecast as to structure when, anticipating the dissection, I declared in favour of an exceptional concentration of the nervous system. Physiology perceived what anatomy had not yet revealed, at all events to my eyes, for since then, on dipping into my books, I have learnt that these anatomical peculiarities, which were then so new to me, are now within the domain of current science. We know that, in the Scarabaeidae, both the larva and the perfect insect are endowed with a concentrated nervous system.

The Garden Scolia attacks Oryctes nasicornis; the Two-banded Scolia the Cetonia; the Interrupted Scolia the Anoxia. All three operate below ground, under the most unfavourable conditions; and all three have for their victim a larva of one of the Scarabaeidae, which, thanks to the exceptional arrangement of its nerve-centres, lends itself, alone of all larvae, to the Wasp's successful enterprises. In the presence of this underground game, so greatly varied in size and shape and yet so judiciously selected to facilitate paralysis, I do not hesitate to generalize and I accept, as the ration of the other Scoliae, larvae of Lamellicorns whose species will be determined by future observation. Perhaps one of them will be found to give chase to the terrible enemy of my crops, the voracious White Worm, the grub of the Cockchafer; perhaps the Hemorrhoidal Scolia, rivalling in size the Garden Scolia and like her, no doubt, requiring a copious diet, will be entered in the insects' "Who's Who" as the destroyer of the Pine-chafer, that magnificent Beetle, flecked with white upon a black or brown ground, who of an evening, during the summer solstice, browses on the foliage of the fir-trees. Though unable to speak with certainty or precision, I am inclined to look upon these devourers of Scarabaeus-grubs as valiant agricultural auxiliaries.