hardly say that, although these lateral inroads are perceptible after
the event, they escape the eye at the moment when they are being
made.

If we would witness them, we must slightly modify the glass
apparatus. I line the inside of the tube with a thick piece of whity-
brown packing-paper, but only over one half of the circumference; the
other half is left bare, so that I may watch the Osmia's attempts.
Well, the captive insect fiercely attacks this lining, which to its
eyes represents the pithy layer of its usual abode; it tears it away
by tiny particles and strives to cut itself a road between the cocoon
and the glass wall. The males, who are a little smaller, have a
better chance of success than the females. Flattening themselves,
making themselves thin, slightly spoiling the shape of the cocoon,
which, however, thanks to its elasticity, soon recovers its first
condition, they slip through the narrow passage and reach the next
cell. The females, when in a hurry to get out, do as much, if they
find the tube at all amenable to the process. But no sooner is the
first partition passed than a second presents itself. This is pierced
in its turn. In the same way will the third be pierced and others
after that, if the insect can manage them, as long as its strength
holds out. Too weak for these repeated borings, the males do not go
far through my thick plugs. If they contrive to cut through the
first, it is as much as they can do; and, even so, they are far from
always succeeding. But, in the conditions presented by the native
stalk, they have only feeble tissues to overcome; and then, slipping,
as I have said, between the cocoon and the wall, which is slightly
worn owing to the circumstances described, they are able to pass
through the remaining occupied chambers and to reach the outside
first, whatever their original place in the stack of cells. It is