iceship, as the experiment with
the native Osmia of the quarries has just proved.

Animal resources have a certain elasticity, within narrow limits. What
we learn from the animals' industry at a given moment is not always the
full measure of their skill. They possess latent powers held in reserve
for certain emergencies. Long generations can succeed one another
without employing them; but, should some circumstance require it,
suddenly those powers burst forth, free of any previous attempts,
even as the spark potentially contained in the flint flashes forth
independently of all preceding gleams. Could one who knew nothing of the
Sparrow but her nest under the eaves suspect the ball-shaped nest at the
top of a tree? Would one who knew nothing of the Osmia save her home
in the Snail-shell expect to see her accept as her dwelling a stump
of reed, a paper funnel, a glass tube? My neighbour the Sparrow,
impulsively taking it into her head to leave the roof for the
plane-tree, the Osmia of the quarries, rejecting her natal cabin, the
spiral of the shell, for my cylinder, alike show us how sudden and
spontaneous are the industrial variations of animals.

CHAPTER 7. ECONOMY OF ENERGY.

What stimulus does the insect obey when it employs the reserve powers
that slumber in its race? Of what use are its industrial variations? The
Osmia will yield us her secret with no great difficulty. Let us examine
her work in a cylindrical habitation. I have described in full detail,
in the foregoing pages, the structure of her nests when the dwelling
adopted is a reed-stump or any other cylinder; and I will content myself
here with recapitulating the essential features of that nest-building.

We must first distinguish three classes of reeds according to their
diameter: the small, the medium-sized and the large. I call small those
whose narrow width just allows the Osmia to go about her household
duties without discomfort. She must be able to turn where she stands
in order to brush her abdomen and rub off its load of pollen, after
disgorging the honey in the centre of the heap of flour already
collected. If the width of the tube does not admit of this operation,
if the insect is obliged to go out and then come in again backwards in
order to place itself in a favourable posture for the discharge of the
pollen, then the reed is too narrow and the Osmia is rather reluctant
to accept it. The middle-sized reeds and a fortiori the large ones l