tuous
passages full of irregular curves; it bends it in an arc which allows
it to turn about; and, with its head held plumb with the adjacent
surface, it goes straight ahead by the nearest way.

The most extraordinary obstacles are powerless to turn it aside from
its plane and its curve, so imperative is its guiding force. It will
gnaw metal, if need be, rather than turn its back upon the light,
which it feels to be close at hand. The entomological records place
this incredible fact beyond a doubt. At the time of the Crimean War,
the Institut de France received some packets of cartridges in which
the bullets had been perforated by _Sirex juvencus_; a little later,
at the Grenoble Arsenal, _S. gigas_ carved himself a similar exit. The
larva was in the wood of the cartridge-boxes; and the adult insect,
faithful to its direction of escape, had bored through the lead
because the nearest daylight was behind that obstacle.

There is an exit-compass, that is incontestable, both for the larvae
preparing the passage of deliverance and for the adult insect, the
Sirex obliged to make that passage for himself. What is it? Here the
problem becomes surrounded with a darkness which is perhaps
impenetrable; we are not well enough equipped with means of receiving
impressions even to imagine the causes which guide the creature. There
is, in certain events, another world of the senses in which our organs
perceive nothing, a world which is closed to us. The eye of the camera
sees the invisible and photographs the image of the ultra-violet rays;
the tympanum of the microphone hears what to us is silence. A
scientific toy, a chemical contrivance surpass us in sensibility.
Would it be rash to attribute similar faculties to the delicate
organization of the insect, even with regard to agencies unknown to
our science, because they do not fall within the domain of our senses?
To this question there is no positive reply; we have suspicions and
nothing more. Let us at least dispel a few false notions that might
occur to us.

Does the wood guide the insect, adult or larva, by its structure?
Gnawed across the grain, it must produce a certain impression; gnawed
lengthwise, it must produce a different impression. Is there not
something here to guide the sapper? No, for in the stump of a tree
left standing the emergence takes place, according to the proximity of
the light, sometimes by way of the horizontal section, by means of a
rectilinear path ru