growing downwards so that the comb has to be built over
one face of the slip--in this case the bees can lay the foundations of one
wall of a new hexagon, in its strictly proper place, projecting beyond the
other completed cells. It suffices that the bees should be enabled to stand
at their proper relative distances from each other and from the walls of
the last completed cells, and then, by striking imaginary spheres, they can
build up a wall intermediate between two adjoining spheres; but, as far as
I have seen, they never gnaw away and finish off the angles of a cell till
a large part both of that cell and of {233} the adjoining cells has been
built. This capacity in bees of laying down under certain circumstances a
rough wall in its proper place between two just-commenced cells, is
important, as it bears on a fact, which seems at first quite subversive of
the foregoing theory; namely, that the cells on the extreme margin of
wasp-combs are sometimes strictly hexagonal; but I have not space here to
enter on this subject. Nor does there seem to me any great difficulty in a
single insect (as in the case of a queen-wasp) making hexagonal cells, if
she work alternately on the inside and outside of two or three cells
commenced at the same time, always standing at the proper relative distance
from the parts of the cells just begun, sweeping spheres or cylinders, and
building up intermediate planes. It is even conceivable that an insect
might, by fixing on a point at which to commence a cell, and then moving
outside, first to one point, and then to five other points, at the proper
relative distances from the central point and from each other, strike the
planes of intersection, and so make an isolated hexagon: but I am not aware
that any such case has been observed; nor would any good be derived from a
single hexagon being built, as in its construction more materials would be
required than for a cylinder.

As natural selection acts only by the accumulation of slight modifications
of structure or instinct, each profitable to the individual under its
conditions of life, it may reasonably be asked, how a long and graduated
succession of modified architectural instincts, all tending towards the
present perfect plan of construction, could have profited the progenitors
of the hive-bee? I think the answer is not difficult: it is known that bees
are often hard pressed to get sufficient nectar; and I am informed by Mr.
Tegetmeier that it