w, then of fine and supple materials which the artisan can
work together in a regular manner, that is to say by felting or
weaving. Facts will show us the successive stages of improvement which
have been introduced into this industry. I will begin with the more
rudimentary.

_Rudiments of this industry._--There are, first, cases in which the
will of the animal does not intervene, or at least is very slightly
manifested. The creature is found covered and protected by foreign
bodies which are often living beings. Spider-crabs (_Maia_), for
example, have their carapaces covered with algae and hydroids of all
sorts. Thus garnished, the Crustaceans have the advantage of not being
recognised from afar when they go hunting, since beneath this fleece
they resemble some rock. H. Fol has observed at Villefranche-sur-Mer a
_Maia_ so buried beneath this vegetation that it was impossible at
first sight to distinguish it from the stones around. Under these
conditions the animal submits to a shelter rather than creates it. Yet
it is not so passive as one might at first be led to suppose. When the
algae which flourish on its back become too long and impede or delay
its progress, it tears them off with its claws and thoroughly cleans
itself. The carapace being quite clean, the animal finds itself too
smooth and too easy to distinguish from surrounding objects; it
therefore takes up again fragments of algae and replaces them where
they do not delay to take root like cuttings and to flourish anew.
This culture is therefore intentional; the crab directs it and arrests
its exuberance; it is no more the victim of it than the gardener is
the slave of the vegetables which he waters day by day. From
generation to generation this crab has acquired the habit, the
instinct if one prefers, of thus covering itself so that it may be
confused with neighbouring objects. Naturally it is ignorant of
botany, and knows nothing of cuttings. If placed in an aquarium with
little fragments of paper it will seize them and place them on its
back, as it would have done with algae, without troubling as to whether
they become fixed or not. In spite of this lack of judgment, we cannot
fail to recognise in this _Maia_ a certain ingenuity in
self-concealment.

[Illustration: FIG. 23.]

The Sponge-crab (_Dromia vulgaris_) also practises this method of
shelter. It seizes a large sponge and maintains it firmly over its
carapace with the help of the posterior pair of