of two excrescences separated by the
mid-dorsal line; the lower ones have not this divided appearance.
These are the organs of locomotion, the ambulacra. When the larva
wishes to move forwards, it expands its hinder ambulacra, those on the
back as well as those on the belly, and contracts its front ones.
Fixed to the side of the narrow gallery by their ridges, the hind-pads
give the grub a purchase. The flattening of the fore-pads, by
decreasing the diameter, allows it to slip forward and to take half a
step. To complete the step, the hind-quarters have to be brought up
the same distance. With this object, the front pads fill out and
provide support, while those behind shrink and leave free scope for
their segments to contract.

With the double support of its back and belly, with alternate puffings
and shrinkings, the animal easily advances or retreats along its
gallery, a sort of mould which the contents fill without a gap. But,
if the locomotory pads grip only on one side, progress becomes
impossible. When placed on the smooth wood of my table, the animal
wriggles slowly; it lengthens and shortens without advancing by a
hair's-breadth. Laid on the surface of a piece of split oak, a rough,
uneven surface, due to the gash made by the wedge, it twists and
writhes, moves the front part of its body very slowly from left to
right and right to left, lifts it a little, lowers it and begins
again. These are the most extensive movements made. The vestigial legs
remain inert and absolutely useless.

Then why are they there? Better to lose them altogether, if it be true
that crawling inside the oak has deprived the animal of the good legs
with which it started. The influence of environment, so well-inspired
in endowing the grub with ambulatory pads, becomes a mockery when it
leaves it these ridiculous stumps. Can the structure, perchance, be
obeying other rules than those of environment?

Though the useless legs, the germs of the future limbs, persist, there
is no sign in the grub of the eyes wherewith the Cerambyx will be
richly gifted. The larva has not the least trace of organs of vision.
What would it do with sight, in the murky thickness of a tree-trunk?
Hearing is likewise absent. In the never-troubled silence of the oak's
inmost heart, the sense of hearing would be a non-sense. Where sounds
are lacking, of what use is the faculty of discerning them? Should
there be any doubts, I will reply to them with the following
e