This apparent fin in reality consists of the two fore-limbs, which, packed in a special sheath, are bent backwards, stretched out against one another in a straight line.

Its small degree of mobility must enable the grub to escape from the egg-shell and, with greater difficulty, from the woody tunnel leading to the open air.
Moving outwards a little from the body, and then moving back again, this lever serves as a means of progression, its terminal hooks being already fairly strong.

The four other feet are still covered by the common envelope, and are absolutely inert.

It is the same with the antennae, which can scarcely be seen through the magnifying-glass.

The organism which has issued from the egg is a boat-shaped body with a fin-shaped limb pointing backwards on the ventral face, formed by the junction of the two fore-limbs.