victualling a cell, it becomes obvious that the total laying must be
kept within narrow bounds and that the mother has no time to lose if she
wishes to get fifteen cells satisfactorily built in three or four weeks
interrupted by compulsory rests. I shall give some facts later which
will dispel your doubts, if any remain.

I assume, therefore, that a number of eggs bordering on fifteen
represents the entire family of an Osmia, as it does of many other Bees.

Let us consult some other complete series. Here are two:

1 2 3 4 5 6 7 8 9 10 11 12 13 F F M F M F M F F F F M F F M F F F M F F
M F M

In both cases, the laying is taken as complete, for the same reasons as
above.

We will end with some series that appear to me incomplete, in view of
the small number of cells and the absence of any free space above the
pile of cocoons:

1 2 3 4 5 6 7 8 M M F M M M M M M M F M F M M M F M F F M M M M M F M F
F F F M M M F M

These examples are more than sufficient. It is quite evident that the
distribution of the sexes is not governed by any rule. All that I can
say on consulting the whole of my notes, which contain a good many
instances of complete layings--most of them, unfortunately, spoilt
through gaps caused by parasites, the death of the larva, the failure of
the egg to hatch and other accidents--all that I can say in general is
that the complete series begins with females and nearly always ends with
males. The incomplete series can teach us nothing in this respect,
for they are only fragments starting we know not whence; and it is
impossible to tell whether they should be ascribed to the beginning, to
the end, or to an intermediate period of the laying. To sum up: in the
laying of the Three-pronged Osmia, no order governs the succession of
the sexes; only, the series has a marked tendency to begin with females
and to finish with males.

The brambles, in my district, harbour two other Osmiae, both of much
smaller size: O. detrita, PEREZ, and O. parvula, DUF. The first is very
common, the second very rare; and until now I have found only one of
her nests, placed above a nest of O. detrita, in the same bramble. Here,
instead of the lack of order in the distribution of the sexes which we
find with O. tridentata, we have an order remarkable for consistency
and simplicity. I have before me the list of the series of O. detrita
collected last winter. Here are some of them:

1. A series of twelve: seven females, beginning