I promised fractions. Here they are. Let us consider the Tarantula and the Epeira on whom the Calicurgi have just operated. The first thrust of the sting is delivered in the mouth. In both victims the poison-fangs are absolutely lifeless: tickling with a bit of straw never once succeeds in making them open. On the other hand, the palpi, their very near neighbours, their adjuncts as it were, possess their customary mobility. Without any previous touches, they keep on moving for weeks. In entering the mouth the sting did not reach the cervical ganglia, or sudden death would have ensued and we should have before our eyes corpses which would go bad in a few days, instead of fresh carcases in which traces of life remain manifest for a long time. The cephalic nerve-centres have been spared.
What is wounded then, to procure this profound inertia of the poison-fangs?
I regret that my anatomical knowledge leaves me undecided on this point.
Are the fangs actuated by a special ganglion? Are they actuated by fibres issuing from centres exercising further functions? I leave to anatomists equipped with more delicate instruments than I the task of elucidating this obscure question. The second conjecture appears to me the more probable, because of the palpi, whose nerves, it seems to me, must have the same origin as those of the fangs. Basing our argument on this latter hypothesis, we see that the Calicurgus has only one means of suppressing the movement of the poisoned pincers without affecting the mobility of the palpi, above all without injuring the cephalic centres and thus producing death, namely, to reach with her sting the two fibres actuating the fangs, fibres as fine as a hair.
I insist upon this point. Despite their extreme delicacy, these two filaments must be injured directly; for, if it were enough for the sting to inject its poison "there or thereabouts," the nerves of the palpi, so close to the first, would undergo the same intoxication as the adjacent region and would leave those appendages motionless. The palpi move; they retain their mobility for a considerable period; the action of the poison, therefore, is evidently situated in the nerves of the fangs. There are two of these nerve-filaments, very fine, very difficult to discover, even by the professional anatomist. The Calicurgus has to reach them one after the other, to moisten them with her poison, possibly to transfix them, in any case to operate upon them in a very restricted manner; so that the diffusion of the virus may not involve the adjoining parts. The extreme delicacy of this surgery explains why the weapon remains in the mouth so long; the point of the sting is seeking and eventually finds the tiny fraction of a millimetre where the poison is to act. This is what we learn from the movements of the palpi close to the motionless fangs; they tell us that the Calicurgi are vivisectors of alarming accuracy.
If we accept the hypothesis of a special nerve-centre for the mandibles, the difficulty would be a little less, without detracting from the operator's talent. The sting would then have to reach a barely visible speck, an atom in which we should hardly find room for the point of a needle. This is the difficulty which the various paralysers solve in ordinary practice. Do they actually wound with their dirks the ganglion whose influence is to be done away with? It is possible, but I have tried no test to make sure, the infinitely tiny wound appearing to be too difficult to detect with the optical instruments at my disposal. Do they confine themselves to lodging their drop of poison on the ganglion, or at all events in its immediate neighbourhood? I do not say no.
I declare moreover, that, to provoke lightning paralysis, the poison, if it is not deposited inside the mass of nervous substance, must act from somewhere very near. This assertion is merely echoing what the Two-banded Scolia has just shown us: her Cetonia-grub, stung less than a millimetre from the regular spot, did not become motionless until next day. There is no doubt, judging by this instance, that the effect of the virus spreads in all directions within a radius of some extent; but this diffusion is not enough for the operator, who requires for her egg, which is soon to be laid, absolute safety from the very first.
On the other hand, the actions of the paralysers argue a precise search for the ganglia, at all events for the first thoracic ganglion, the most important of all. The Hairy Ammophila, among others, affords us an excellent example of this method. Her three thrusts in the caterpillar's thorax and especially the last, between the first and second pair of legs, are more prolonged than the stabs distributed among the abdominal ganglia.
Everything justifies us in believing that, for these decisive inoculations, the sting seeks out the corresponding ganglion and acts only when it finds it under its point. On the abdomen this peculiar insistence ceases; the sting passes swiftly from one segment to another. For these segments, which are less dangerous, the Ammophila perhaps relies on the diffusion of her venom; in any case, the injections, though hastily administered, do not diverge from a close vicinity of the ganglia, for their field of action is very limited, as is proved by the number of inoculations necessary to induce complete torpor, or, more simply, by the following example.
