eir 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 explain the
mother's hesitation and her obstinacy in settling females in some of my
apparatus which looked as if they could suit none but males.

A suspicion occurs to me, a suspicion aroused by my attentive
examination of the narrow tubes. All, whatever the number of their
inmates, are carefully plugged at the opening, just as separate tubes
would be. It might therefore be the case that the narrow gallery at the
back was looked upon by the Osmia not as the prolongation of the large
front gallery, but as an independent tube. The facility with which the
worker turns as soon as she reaches the wide tube, her liberty of
action, which is now as great as in a doorway communicating with the
outer air, might well be misleading and cause the Osmia to treat the
narrow passage at the back as though the wide passage in front did not
exist. This would account for the placing of the female in the large
tube above the males in the small tube, an arrangement contrary to her
custom.

I will not undertake to decide whether the mother really appreciates
the danger of my snares, or whether she makes a mistake in considering
only the space at her disposal and beginning with males, who are liable
to remain imprisoned. At any rate, I perceive a tendency to deviate as
little as possible from the order which safeguards the emergence of
both sexes. This tendency is demonstrated by her repugnance to
colonizing my narrow tubes with long series of males. However, so far
as we are concerned, it does not matter much what passes at such times
in the Osmia's little brain. Enough for us to know that she dislikes
narrow and long tubes, not because they are narrow, but because they
are at the same time long.

And, in fact, she does very well with a short tube of the same
diameter. Such are the cells in the old nests of the Mason-bee of the
Shrubs and the empty shells of the Garden Snail. With the short tube
the two disadvantages of the long tube are avoided. She has very little
of