icent specimen. The curves, of which I
uncover a layer at every stroke of the plane, far exceed my
requirements; they are strikingly regular; they afford the compasses
the full space needed for accurate measurement.

Before calling in geometry, let us, if possible, name the creator of
these beautiful curves. The inhabitants of the poplar have
disappeared, perhaps long ago, as is proved by the mycelium of the
agaric; the insect would not gnaw and bore its way through timber all
permeated with the felt-like growth of the cryptogam. A few weaklings,
however, have died without being able to escape. I find their remains
swathed in mycelium. The agaric has preserved them from destruction by
wrapping them in tight cerements. Under these mummy-bandages, I
recognise a Saw-fly, _Sirex augur_, KLUG., in the state of the perfect
insect. And--this is an important detail--all these adult remains,
without a single exception, occupy spots which have no means of
communication with the outside. I find them sometimes in a
partly-constructed curved passage, beyond which the wood remains
intact, sometimes at the end of the straight central gallery, choked
with sawdust, which is not continued in front. These remains, with no
thoroughfare before them, tell us plainly that the Sirex adopts for
its exit methods not employed by the Buprestes and the Longicorns.

The larva does not prepare the path of deliverance; it is left for the
perfect insect to open itself a passage through the wood. What I have
before my eyes tells me more or less plainly the sequence of events.
The larva, whose presence is proved by galleries blocked with packed
sawdust, do not leave the centre of the trunk, a quieter retreat, less
subject to the vicissitudes of the climate. Metamorphosis is effected
at the junction of the straight gallery and the curved passage which
is not yet made. When strength comes, the perfect insect tunnels ahead
for a distance of more than four inches and opens up the exit-passage,
which I find choked, not with compact sawdust, but with loose powdery
rubbish. The dead insects which I strip of their mycelium-shrouds are
weaklings whose strength deserted them mid-way. The rest of the
passage is lacking because the labourer died on the road.

With this fact of the insect itself boring the exit passage, the
problem assumes a more troublesome form. If the larva, rich in leisure
and satisfied with its sojourn in the interior of the trunk,
simplifies