edge. When the dwelling is thus prepared and
provisioned, the insect lays an egg there and closes the upper part
with a vault, built by successive deposits over the opening, which is
more and more narrowed until it is finally shut up. Having completed a
chamber, it passes on to the next, and so on until it has assured the
fate of all its descendants.

This hymenopterous insect certainly shows in its acts as an artisan an
inevitable instinct: hereditary intelligence has become less personal
and less spontaneous. In certain cases, however, the instinct loses
its rigidity and automatism. Thus, when a _Chalicodoma_, at the moment
of preparing to accomplish its task, finds an old nest, still capable
of repair although dilapidated, it does not hesitate to take
possession of it and to silence its assumed innate instinct of
building. It profits by the work already done, and is content to fill
up the cracks or to re-establish the masonry where defective; then it
provisions the renewed cells with honey, and lays its eggs in them. In
certain circumstances it shows itself still more sparing of trouble,
and boldly rebels against the law which seems to be imposed on it by
nature. If it feels itself sufficiently strong, the _Chalicodoma_
throws itself on one of its fellows, a peaceful constructor that has
almost completed its work; it chases it away, and takes possession of
its property to shelter its own eggs. Instead of manufacturing the
cell from bottom to top, it has only to complete it. Such acts
evidently show the reflection appearing through instinct.

Besides the Swallows, of which I have already spoken, birds offer us
several types of skilful construction with tempered earth.

The Flamingo, which lives in marshes, cannot place its eggs on the
earth nor in the trunks of trees, which are often absent from its
domain. It builds a cone of mud, which dries and becomes very
resistant, and it prepares at the summit an excavation open to the
air; this is the nest. The female broods by sitting with her legs
hanging over the sides of the hillock on which her little family
prospers above the waters and the damp soil.

A Perch in the Danube also manufactures a dwelling of dried earth. It
gives it the form of an elliptic cupola, and prepares a semicircular
opening for entry and exit.

The bird which shows itself the most skilful mason is probably the
Oven-Bird (_Furnarius rufus_) of Brazil and La Plata. Its name is
owing to the form