no matter what
period, from the beginning to the end of the operations. The series
which, according to rule, would begin with females now begins with
males. Once the larger gallery is reached, the laying is pursued in the
usual order.

We have advanced one step and that no small one: we have seen that the
Osmia, when circumstances require it, is capable of reversing the
sequence of the sexes. Would it be possible, provided that the tube
were long enough, to obtain a complete inversion, in which the entire
series of the males should occupy the narrow gallery at the back and
the entire series of the females the roomy gallery in front? I think
not; and I will tell you why.

Long and narrow cylinders are by no means to the Osmia's taste, not
because of their narrowness but because of their length. Observe that
for each load of honey brought the worker is obliged to move backwards
twice. She enters, head first, to begin by disgorging the honey-syrup
from her crop. Unable to turn in a passage which she blocks entirely,
she goes out backwards, crawling rather than walking, a laborious
performance on the polished surface of the glass and a performance
which, with any other surface, would still be very awkward, as the
wings are bound to rub against the wall with their free end and are
liable to get rumpled or bent. She goes out backwards, reaches the
outside, turns round and goes in again, but this time the opposite way,
so as to brush off the load of pollen from her abdomen on to the heap.
If the gallery is at all long, this crawling backwards becomes
troublesome after a time; and the Osmia soon abandons a passage that is
too small to allow of free movement. I have said that the narrow tubes
of my apparatus are, for the most part, only very incompletely
colonized. The Bee, after lodging a small number of males in them,
hastens to leave them. In the wide front gallery she can stay where she
is and still be able to turn round easily for her different
manipulations; she will avoid those two long journeys backwards, which
are so exhausting and so bad for her wings.

Another reason no doubt prompts her not to make too great a use of the
narrow passage, in which she would establish males, followed by females
in the part where the gallery widens. The males have to leave their
cells a couple of weeks or more before the females. If they occupy the
back of the house they will die prisoners or else they will overturn
everything on th