of all shapes and sizes. There are long and short ones,
spacious ones and narrow. Short of expatriating herself, a Spartan
course, she has to use them all, from first to last, for she has no
choice. Guided by these considerations, I embarked on the experiments
which I will now describe.

I have said how my study became a populous hive, in which the
Three-horned Osmia built her nests in the various appliances which I
had prepared for her. Among these appliances, tubes, either of glass or
reed, predominated. There were tubes of all lengths and widths. In the
long tubes, entire or almost entire layings, with a series of females
followed by a series of males, were deposited. As I have already
referred to this result, I will not discuss it again. The short tubes
were sufficiently varied in length to lodge one or other portion of the
total laying. Basing my calculations on the respective lengths of the
cocoons of the two sexes, on the thickness of the partitions and the
final lid, I shortened some of these to the exact dimensions required
for two cocoons only, of different sexes.

Well, these short tubes, whether of glass or reed, were seized upon as
eagerly as the long tubes. Moreover, they yielded this splendid result:
their contents, only a part of the total laying, always began with
female and ended with male cocoons. This order was invariable; what
varied was the number of cells in the long tubes and the proportion
between the two sorts of cocoons, sometimes males predominating and
sometimes females.

When confronted with tubes too small to receive all her family, the
Osmia is in the same plight as the Mason-bee in the presence of an old
nest. She thereupon acts exactly as the Chalicodoma does. She breaks up
her laying, divides it into series as short as the room at her disposal
demands; and each series begins with females and ends with males. This
breaking up, on the one hand, into sections in all of which both sexes
are represented and the division, on the other hand, of the entire
laying into just two groups, one female, the other male, when the
length of the tube permits, surely provide us with ample evidence of
the insect's power to regulate the sex of the egg according to the
exigencies of space.

And besides the exigencies of space one might perhaps venture to add
those connected with the earlier development of the males. These burst
their cocoons a couple of weeks or more before the females; they are
the fir