of the laying into couples
and this alternation of the males and females. Without calling for other
work than the transverse partitions, the broadening stairway of the
Snail-shell thus furnishes both sexes with house-room suited to their
size.

The second Resin-bee that inhabits shells, Anthidium bellicosum, hatches
in July and works during the fierce heat of August. Her architecture
differs in no wise from that of her kinswoman of the springtime, so much
so that, when we find a tenanted Snail-shell in a hole in the wall or
under the stones, it is impossible to decide to which of the two species
the nest belongs. The only way to obtain exact information is to break
the shell and split the cocoons in February, at which time the nests
of the summer Resin-bee are occupied by larvae and those of the spring
Resin-bee by the perfect insect. If we shrink from this brutal
method, we are still in doubt until the cocoons open, so great is the
resemblance between the two pieces of work.

In both cases, we find the same lodging, Snail-shells of every size and
every kind, just as they happen to come; the same resin lid, the inside
gritty with tiny bits of stone, the outside almost smooth and
sometimes ornamented with little shells; the same barricade--not always
present--of various kinds of rubbish; the same division into two rooms
of unequal size occupied by the two sexes. Everything is identical, down
to the purveyor of the gum, the brown-berried juniper. To say more about
the nest of the summer Resin-bee would be to repeat oneself.

There is only one thing that requires further investigation. I do not
see the reason that prompts the two insects to leave the greater part of
their shell empty in front, instead of occupying it entirely up to the
orifice as the Osmia habitually does. As the mother's laying is broken
up into intermittent shifts of a couple of eggs apiece, is it necessary
that there should be a new home for each shift? Is the half-fluid resin
unsuitable for the wide-spanned roofs which would have to be constructed
when the diameter of the helical passage exceeded certain limits? Is
the gathering of the cement too wearisome a task to leave the Bee any
strength for making the numerous partitions which she would need if she
utilized the spacious final whorl? I find no answer to these questions.
I note the fact without interpreting it: when the shell is a large one,
the front part, almost the whole of the last whorl, re