These animals are
excessively sluggish and defenceless, and the power of changing their
colour to that of their immediate surroundings is no doubt of great
service to them. Many of the flatfish are also capable of changing their
colour according to the colour of the bottom they rest on; and frogs
have a similar power to a limited extent. Some crustacea also change
colour, and the power is much developed in the Chameleon shrimp (Mysis
Chamaeleon) which is gray when on sand, but brown or green when among
brown or green seaweed. It has been proved by experiment that when this
animal is blinded the change does not occur. In all these cases,
therefore, we have some form of reflex or sense action by which the
change is produced, probably by means of pigment cells beneath the skin
as in the chameleon.
The second class consists of certain larvae, and pupae, which undergo
changes of colour when exposed to differently coloured surroundings.
This subject has been carefully investigated by Mr. E.B. Poulton, who
has communicated the results of his experiments to the Royal
Society.
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