ll that I had
to do was to hang up some bramble-stumps as I found them, vertically,
but with the opening downwards. Out of two stalks thus arranged and
peopled with Osmiae, not one of the insects succeeded in emerging. All
the Bees died in the shaft, some turned upwards, others downwards.
On the other hand, three stems occupied by Anthidia discharged their
population safe and sound. The outgoing was effected at the bottom, from
first to last, without the least impediment. Must we take it that
the two sorts of Bees are not equally sensitive to the influences of
gravity? Can the Anthidium, built to pass through the difficult obstacle
of her cotton wallets, be better-adapted than the Osmia to make her way
through the wreckage that keeps falling under the worker's feet; or,
rather, may not this very cotton-waste put a stop to these cataracts of
rubbish which must naturally drive the insect back? This is all quite
possible; but I can say nothing for certain.

Let us now experiment with vertical tubes open at both ends. The
arrangements, save for the upper orifice, are the same as before. The
cocoons, in some of the tubes, have their heads turned down; others,
up; in others again, their positions alternate. The result is similar to
what we have seen above. A few Osmiae, those nearest the bottom orifice,
take the lower road, whatever the direction first occupied by the
cocoon; the others, composing by far the larger number, take the higher
road, even when the cocoon is placed upside down. As both doors are
free, the outgoing is effected at either end with success.

What are we to conclude from all these experiments? First, that gravity
guides the insect towards the top, where the natural door is, and makes
it turn in its cell when the cocoon has been reversed. Secondly, I seem
to suspect an atmospheric influence and, in any case, some second cause
that sends the insect to the outlet. Let us admit that this cause is
the proximity of the outer air acting upon the anchorite through the
partitions.

The animal then is subject, on the one hand, to the promptings of
gravity, and this to an equal degree for all, whatever the storey
inhabited. Gravity is the common guide of the whole series from base to
top. But those in the lower boxes have a second guide, when the bottom
end is open. This is the stimulus of the adjacent air, a more powerful
stimulus than that of gravity. The access of the air from without is
very slight, because