m
(eating at the same table) suggests, the partnership is _mutually_
beneficial. For the sea-anemone is carried about by the hermit-crab, and
it doubtless gets its share of crumbs from its partner's frequent meals.
There is a very interesting sidelight on the mutual benefit in the case
of a dislodged sea-anemone which sulked for a while and then waited in a
state of preparedness until a hermit-crab passed by and touched it.
Whereupon the sea-anemone gripped and slowly worked itself up on to the
back of the shell.

Sec. 6

Other Kinds of Elusiveness

There are various kinds of disguise which are not readily classified. A
troop of cuttlefish swimming in the sea is a beautiful sight. They keep
time with one another in their movements and they show the same change
of colour almost at the same moment. They are suddenly attacked,
however, by a small shark, and then comes a simultaneous discharge of
sepia from their ink-bags. There are clouds of ink in the clear water,
for, as Professor Hickson puts it, the cuttlefishes have thrown dust in
the eyes of their enemies. One can see a newborn cuttlefish do this a
minute after it escapes from the egg.

Very beautiful is the way in which many birds, like our common
chaffinch, disguise the outside of their nest with moss and lichen and
other trifles felted together, so that the cradle is as inconspicuous as
possible. There seems to be a touch of art in fastening pieces of
spider's web on the outside of a nest!

How curious is the case of the tree-sloth of South American forests,
that walks slowly, back downwards, along the undersides of the branches,
hanging on by its long, curved fingers and toes. It is a nocturnal
animal, and therefore not in special danger, but when resting during the
day it is almost invisible because its shaggy hair is so like certain
lichens and other growths on the branches. But the protective
resemblance is enhanced by the presence of a green alga, which actually
lives on the surface of the sloth's hairs--an alga like the one that
makes tree-stems and gate-posts green in damp weather.

There is no commoner sight in the early summer than the cuckoo-spit on
the grasses and herbage by the wayside. It is conspicuous and yet it is
said to be left severely alone by almost all creatures. In some way it
must be a disguise. It is a sort of soap made by the activity of small
frog-hoppers while they are still in the wingless larval stage, before
they begin to h