that, in the Mason-bee, the
females take the lead in the order of primogeniture. Theirs is the
central and best-protected part of the clay fortress; the outer part,
that most exposed to the inclemencies of the weather and to accidents,
is for the males.

The males' cells do not differ from the females' only by being placed at
the outside of the cluster; they differ also in their capacity, which is
much smaller. To estimate the respective capacities of the two sorts
of cells, I go to work as follows: I fill the empty cell with very fine
sand and pour this sand back into a glass tube measuring 5 millimetres
(.195 inch.--Translator's Note.) in diameter. From the height of the
column of sand we can estimate the comparative capacity of the two kinds
of cells. I will take one at random among my numerous examples of cells
thus gauged.

It comprises thirteen cells and occupies a dihedral angle. The female
cells give me the following figures, in millimetres, as the height of
the columns of sand:

40, 44, 43, 48, 48, 46, 47 (1.56, 1.71, 1.67, 1.87, 1.87, 1.79, 1.83
inches.--Translator's Note.),

averaging 45. (1.75 inches.--Translator's Note.)

The male cells give me:

32, 35, 28, 30, 30, 31 (1.24, 1.36, 1.09, 1.17, 1.17, 1.21
inches.--Translator's Note.),

averaging 31. (1.21 inches.--Translator's Note.)

The ratio of the capacity of the cells for the two sexes is therefore
roughly a ratio of 4 to 3. The actual contents of the cell being
proportionate to its capacity, the above ratio must also be more or
less the ratio of provisions and sizes between females and males. These
figures will assist us presently to tell whether an old cell, occupied
for a second or third time, belonged originally to a female or a male.

The Chalicodoma of the Sheds cannot give us any information on this
matter. She builds under the same eaves, in excessively populous
colonies; and it is impossible to follow the labours of any single
Mason, whose cells, distributed here and there, are soon covered up
with the work of her neighbours. All is muddle and confusion in the
individual output of the swarming throng.

I have not watched the work of the Chalicodoma of the Shrubs with close
enough attention to be able to state definitely that this Bee is a
solitary builder. Her nest is a ball of clay hanging from a bough.
Sometimes, this nest is the size of a large walnut and then appears to
be the work of one alone; sometimes, it is the size of a m