289-313.

_Burrows with barns adjoined._--Certain Rodents have carried hollow
dwellings to great perfection. Among these the Hamster of Germany
(_Cricetus frumentarius_) is not the least ingenious. To his
dwelling-room he adds three or four storehouses for the amassed
provisions of which I have already had occasion to speak. The burrow
possesses two openings: one, which the animal prefers to use, which
sinks vertically into the soil; the other, the passage of exit with a
gentle and very winding slope. The bottom of the central room is
carpeted with moss and straw, which make it a warm and pleasant home.
A third tunnel starts from this sleeping chamber, soon forking and
leading to the wheat barns. Thus during the winter the Hamster has no
pressing need to go out except on fine days for a little fresh air. He
has everything within his reach, and can remain shut up with nothing
to fear from the severity of the season.

_Dwellings hollowed out in wood._--It is not only the soil which may
serve for retreat; wood serves as an asylum for numerous animals, who
bore it, and find in it both food and shelter. In this class must be
placed a large number of Worms, Insects, and Crustaceans. One of these
last, the _Chelura terebrans_, a little Amphipod, constitutes a great
danger for the works of man. It attacks piles sunken to support
structures, and undermines them to such a degree that they eventually
fall. Wood is formed of concentric layers alternately composed of
large vessels formed during the summer, and smaller vessels formed
during the winter. The latter zones are more resistant, the former are
softer. When one of these Crustaceans attacks a pile, it first bores a
little horizontal passage, stopping at a layer of summer-growth. It
there hollows a large grotto, leaving here and there pillars of
support. It lays in this space. The new generation working around the
parents increases the space and feeds on the wood removed. A second
generation is produced, and the inhabitants become pressed for space.
The new-born pierce numerous passages and penetrate towards the
interior of the pile as far as the next summer layer. There they
spread themselves, always boring; they construct new rooms like the
first, and arrange pillars here and there. Their descendants gain the
subjacent zone, and so the process goes on. During this time the early
ancestors who hollowed the surface dwellings have died, and the holes
which they made are no l