We will linger over this problem no longer. Let us observe the grub
which has now become the sole tenant of the pea by the death of its
brothers. It has had no part in their death; chance has favored it, that
is all. In the centre of the pea, a wealthy solitude, it performs the
duty of a grub, the sole duty of eating. It nibbles the walls enclosing
it, enlarging its lodgment, which is always entirely filled by its
corpulent body. It is well shaped, fat, and shining with health. If I
disturb it, it turns gently in its niche and sways its head. This is its
manner of complaining of my importunities. Let us leave it in peace.

It profits so greatly and so swiftly by its position that by the time
the dog-days have come it is already preparing for its approaching
liberation. The adult is not sufficiently well equipped to open for
itself a way out through the pea, which is now completely hardened. The
larva knows of this future helplessness, and with consummate art
provides for its release. With its powerful mandibles it bores a channel
of exit, exactly round, with extremely clean-cut sides. The most skilful
ivory-carver could do no better.

To prepare the door of exit in advance is not enough; the grub must also
provide for the tranquillity essential to the delicate processes of
nymphosis. An intruder might enter by the open door and injure the
helpless nymph. This passage must therefore remain closed. But how?

As the grub bores the passage of exit, it consumes the farinaceous
matter without leaving a crumb. Having come to the skin of the pea, it
stops short. This membrane, semi-translucid, is the door to the chamber
of metamorphosis, its protection against the evil intentions of external
creatures.