branchial respiration. From
time to time it cleans out the dirt and rubbish which accumulate in
the hole. It makes a little pile of all the refuse which it finds,
and, seizing it between its claws and abdomen, carries it outside.
Executing several journeys very rapidly, it soon clears out its
dwelling.

The dipnoid _Protopterus_, which inhabits the marshes of Senegal and
Gambia, is curious in more than one respect. Firstly, it can breathe
oxygen, whether, like other fish, it finds it dissolved in water or in
the atmospheric air. When during the summer the marshes in which it
lives dry up, it takes refuge in the mud at the bottom, which hardens
and imprisons it, and it thus remains curled up until the time when
the water after the rainy season has softened the earth which
surrounds it. This fact had been known for some time; travellers had
brought back lumps of dried earth of varied size, the largest about as
big as two fists. On opening them the same fish was always found
within, and the chamber in which it is contained was lined with a sort
of cocoon, having the appearance of dry gelatine. Dumeril was able to
observe one of these animals in captivity. At the period corresponding
to the dry period of its own country, the _Protopterus_ buried itself
in the mud which had been placed at the bottom of the aquarium. In
order to realise the conditions found in nature, the water which
covered it was gradually withdrawn. The earth hardened in drying, and
when broken the recluse was seen surrounded by hardened mucus, exactly
like those which came from Senegal.

_Carefully-disposed burrows._--All the cases which we have considered
show us the industry of the hollowed dwelling in its primitive state;
but other animals know how to furnish it with greater luxury. I will
continue in the same order of increasing complication. Many beings
live permanently in a burrow; Reptiles--Snakes or Lizards--are to be
placed among these. Among others, the _Lacerta stirpium_ arranges a
narrow and deep hole, well hidden beneath a thicket, and retires into
it for the winter, when cold renders it incapable of movement and at
the mercy of its enemies. Before giving itself up to its hybernal
sleep, it is careful to close hermetically the opening of the dwelling
with a little earth and dried leaves. When spring returns and the heat
awakens the reptile, it comes out to warm itself and to hunt, but
never abandons its dwelling, always retiring into it in