om the
brain, instead of passing down the spinal cord, the message travels down
the chain of sympathetic ganglia. From these it passes along the nerves
which comes out of the spinal cord and control the skin. Thus the
message reaches the colour-cells in the skin, and before you have
carefully read these lines the flat-fish has slipped on its Gyges ring
and become invisible.

The same power of rapid colour-change is seen in cuttlefishes, where it
is often an expression of nervous excitement, though it sometimes helps
to conceal. It occurs with much subtlety in the AEsop prawn, Hippolyte,
which may be brown on a brown seaweed, green on sea-lettuce or
sea-grass, red on red seaweed, and so on through an extensive repertory.

According to the nature of the background, [Professor Gamble writes]
so is the mixture of the pigments compounded so as to form a close
reproduction both of its colour and its pattern. A sweep of the
shrimp net detaches a battalion of these sleeping prawns, and if
we turn the motley into a dish and give a choice of seaweed, each
variety after its kind will select the one with which it agrees in
colour, and vanish. Both when young and when full-grown, the AEsop
prawn takes on the colour of its immediate surroundings. At
nightfall Hippolyte, of whatever colour, changes to a transparent
azure blue: its stolidity gives place to a nervous restlessness; at
the least tremor it leaps violently, and often swims actively from
one food-plant to another. This blue fit lasts till daybreak, and is
then succeeded by the prawn's diurnal tint.

Thus, Professor Gamble continues, the colour of an animal may express a
nervous rhythm.

[Illustration: _Photo: J. J. Ward, F.E.S._

PROTECTIVE RESEMBLANCE

Hawk Moth, settled down on a branch, and very difficult to detect as
long as it remains stationary. Note its remarkable sucking tongue, which
is about twice the length of its body. The tongue can be quickly coiled
up and put safely away beneath the lower part of the head.]

[Illustration: WHEN ONLY A FEW DAYS OLD, YOUNG BITTERN BEGIN TO STRIKE
THE SAME ATTITUDE AS THEIR PARENTS THRUSTING THEIR BILLS UPWARDS AND
DRAWING THEIR BODIES UP SO THAT THEY RESEMBLE A BUNCH OF REEDS

The soft browns and blue-greens harmonise with the dull sheaths of the
young reeds; the nestling bittern is thus completely camouflaged.]

The Case of Chameleons

The highest level at which