of the partitions; while it can be felt in the
nethermost cells, it must decrease rapidly as the storeys ascend.
Wherefore the bottom insects, very few in number, obeying the
preponderant influence, that of the atmosphere, make for the lower
outlet and reverse, if necessary, their original position; those above,
on the contrary, who form the great majority, being guided only by
gravity when the upper end is closed, make for that upper end. It goes
without saying that, if the upper end be open at the same time as the
other, the occupants of the top storeys will have a double incentive to
take the ascending path, though this will not prevent the dwellers on
the lower floors from obeying, by preference, the call of the adjacent
air and adopting the downward road.

I have one means left whereby to judge of the value of my explanation,
namely, to experiment with tubes open at both ends and lying
horizontally. The horizontal position has a twofold advantage. In
the first place, it removes the insect from the influence of gravity,
inasmuch as it leaves it indifferent to the direction to be taken, the
right or the left. In the second place, it does away with the descent
of the rubbish which, falling under the worker's feet when the boring is
done from below, sooner or later discourages her and makes her abandon
her enterprise.

There are a few precautions to be observed for the successful conduct of
the experiment; I recommend them to any one who might care to make the
attempt. It is even advisable to remember them in the case of the tests
which I have already described. The males, those puny creatures, not
built for work, are sorry labourers when confronted with my stout disks.
Most of them perish miserably in their glass cells, without succeeding
in piercing their partitions right through. Moreover, instinct has been
less generous to them than to the females. Their corpses, interspersed
here and there in the series of the cells, are disturbing causes,
which it is wise to eliminate. I therefore choose the larger, more
powerful-looking cocoons. These, except for an occasional unavoidable
error, belong to females. I pack them in tubes, sometimes varying their
position in every way, sometimes giving them all a like arrangement.
It does not matter whether the whole series comes from one and the same
bramble-stump or from several: we are free to choose where we please;
the result will not be altered.

The first time that I prepa