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When, starting from a position parallel with the axis of the tree, the Sirex has passed gradually to a transversal position, he completes his course in a straight line, which is the shortest road. Does the trajectory imply the minimum of work? Yes, under the conditions of the insect's existence.
On the other hand, in the Tenthredinidae the males are generally darker than the females. In the Siricidae the sexes frequently differ; thus the male of Sirex juvencus is banded with orange, whilst the female is dark purple; but it is difficult to say which sex is the more ornamented. In Tremex columbae the female is much brighter coloured than the male. I am informed by Mr.
To simplify the explanation, we may liken the insect to a section of an inflexible straight line. Let us return to the Sirex, reduced by abstraction to its axis. The metamorphosis is effected not far from the centre of the trunk. The insect lies lengthwise in the tree with its head up, very rarely with its head down. It must reach the outside as quickly as possible.
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 larvæ preparing the passage of deliverance and for the adult insect, the Sirex obliged to make that passage for himself. What is it?
But reasons of convenience whereof the grub is the sole judge, reasons dictated perhaps by weight, cause the vertical to precede the horizontal position. In order to pass from the former to the latter, the insect veers round by describing the arc of a circle. When this turn has been effected, the distance is completed in a straight line. Let us consider the Sirex at his starting-point.
Simiadae, their origin and divisions. Similarity, sexual. Singing of the Cicadae and Fulgoridae; of tree-frogs; of birds, object of the. Sirenia, nakedness of. Sirex juvencus. Siricidae, difference of the sexes in. Siskin, pairing with a canary. Sitana, throat-pouch of the males of. Size, relative, of the sexes of insects. Skin, dark colour of, a protection against heat.
Not so. The sound of what, in the silence of solitude? And are the noises of the outside world propagated through half an inch of wood in such a way as to make differences perceptible? Can it be weight? No again, for the trunk of the poplar shows us more than one Sirex travelling upside down, with his head towards the ground, without any change in the direction of the curved passages.
The problem of the Sirex is now solved. The trajectory is composed of equal elements, with an invariable angle between them; it is the curve whose tangents, divided by infinitely small distances, retain the same inclination between each one and the next; the curve, in a word, with a constant angle of contingence. This characteristic betrays the circumference of the circle.
In brief, the Sirex' gallery is contained in a plane pointing towards the axis of the tree and the starting-point; and of the two portions of this plane the channel passes through the less extensive. Under the conditions, therefore, imposed upon him by his stiffness the hermit of the poplar-tree releases himself with the minimum of mechanical labour.
Instructed by the Sirex, the Buprestes, the Longicorns, I am once again compelled to make the same suggestion. It is not that I care for the expression: the unknown cannot be named in any language. It means that the hermits in the dark know how to find the light by the shortest road; it is the confessions of an ignorance which no honest observer will blush to share.
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