ersion, 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. Remember 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 their way out. This risk is avoided by the order which the
Osmia adopts.

In my tubes with their unusual arrangement, the mother might well find
the dilemma perplexing: there is the narrowness of the space at her
disposal and there is the emergence later on. In the narrow tubes, the
width is insufficient for the females; on the other hand, if she lodges
males there, they are liable to perish, since they will be prevented
from issuing at the proper moment. This would perhaps expla