o the end of the chapter. In the present Essay the subjects dealt
with are nest-making instincts, including the egg-hatching habit of
the Australian bush-turkey. The power of "shamming death."
"Faculty" in relation to instinct. The instinct of lapse of time,
and of direction. Bees' cells very briefly given. Birds feeding
their young on food differing from their own natural food. In the
_Origin_, Ed. i., the cases discussed are the instinct of laying
eggs in other birds' nests; the slave-making instinct in ants; the
construction of the bee's comb, very fully discussed.

First, to take the case of birds'-nests; of existing species (almost
infinitely few in comparison with the multitude which must have existed,
since the period of the new Red Sandstone of N. America, of whose habits
we must always remain ignorant) a tolerably perfect series could be made
from eggs laid on the bare ground, to others with a few sticks just
laid round them, to a simple nest like the wood-pigeons, to others more
and more complicated: now if, as is asserted, there occasionally exist
slight differences in the building powers of an individual, and if,
which is at least probable, that such differences would tend to be
inherited, then we can see that it is at least _possible_ that the
nidificatory instincts may have been acquired by the gradual selection,
during thousands and thousands of generations, of the eggs and young of
those individuals, whose nests were in some degree better adapted to the
preservation of their young, under the then existing conditions. One of
the most surprising instincts on record is that of the Australian
bush-turkey, whose eggs are hatched by the heat generated from a huge
pile of fermenting materials, which it heaps together; but here the
habits of an allied species show how this instinct _might possibly_ have
been acquired. This second species inhabits a tropical district, where
the heat of the sun is sufficient to hatch its eggs; this bird, burying
its eggs, apparently for concealment, under a lesser heap of rubbish,
but of a dry nature, so as not to ferment. Now suppose this bird to
range slowly into a climate which was cooler, and where leaves were more
abundant, in that case, those individuals, which chanced to have their
collecting instinct strongest developed, would make a somewhat larger
pile, and the eggs, aided during some colder season, under the slightly
cooler climate