As soon as the egg arrives
at the cloaca one of the feet seizes it and lowers it gently into the
nest, while the second foot seizes another egg, which during this time
had appeared at the orifice. This manipulation lasts until the end of
the operation, when the tortoise buries all its family, and to flatten
the prominence which results she strikes it repeatedly with her
plastron, raising herself on her legs.

It is not only land animals which adopt this custom of living in the
earth, and there sheltering their offspring. Fish also make retreats
on the bank or at the bottom. To mention only one case, the Bullhead
(_Cottus gobio_) of our rivers, which spawns in the Seine in May,
June, and July, acts in this manner. Beneath a rock in the sand it
prepares a cavity; then seeks females and brings them to lay eggs in
its little lodging. During the four or five weeks before they come out
it watches the eggs, keeping away as far as possible every danger
which threatens them. It only leaves its position when pressed by
hunger, and as soon as the hunt is concluded, returns to the post of
duty.

Other animals when digging have a double object; they wish to shelter
themselves, and at the same time to find the water which they need for
themselves or for the development of their young.

It is well known that Frogs and Toads generally go in the spring to
lay their eggs in streams and ponds. A Batrachian of Brazil and the
hot regions of South America, the _Cystignathus ocellatus_, no doubt
fearing too many dangers for the spawn if deposited in the open water,
employs the artifice of hollowing, not far from the bank, a hole the
bottom of which is filled by infiltration. It there places its eggs,
and the little ones on their birth can lead an aquatic life while
being guaranteed against its risks.

A terrestrial Crab, the _Cardisoma carnifex_, found in Bengal and the
Antilles, acts in the same manner; but in this case it has in view its
own convenience and not care for its offspring. Its habitat is
especially in low-lying spots near the shore, where water may be found
at a trifling depth beneath the soil. To establish its dwelling, the
Crustacean first buries itself until it reaches the liquid level.
Arrived at this point, it makes a large lair in the soft soil, and
effects communication with the outside by various openings. It can
thus easily come and go and retire into its cave, where it finds
security and a humidity favourable for