It passes from end to end through the body of the pioneer, yields during its passage its meagre nutritive principles, and accumulates behind it, obstructing the passage, by which the larva will never return.

The work of extreme division, effected partly by the mandibles and partly by the stomach, makes the digested material more compact than the intact wood, from which it follows that there is always a little free space at the head of the gallery, in which the caterpillar works and lives; it is not of any great length, but just suffices for the movements of the prisoner.
Must not the larva of the Cigale bore its passage in some such fashion?
I do not mean that the results of excavation pass through its body--for earth, even the softest mould, could form no possible part of its diet.
But is not the material detached simply thrust back behind the excavator as the work progresses?
The Cigale passes four years under ground.

This long life is not spent, of course, at the bottom of the well I have just described; that is merely a resting-place preparatory to its appearance on the face of the earth.

The larva comes from elsewhere; doubtless from a considerable distance.

It is a vagabond, roaming from one root to another and implanting its rostrum.