n certain cases the adventitious colour may be
dissolved in the blood or secreted in superficial cells of the body:
thus certain insects make use of the chlorophyll of their food (Poulton,
_Proc. Roy. Soc._ liv. 417). The most perfect cryptic powers are
possessed by those animals in which the individuals can change their
colours into any tint which would be appropriate to a normal
environment. This power is widely prevalent in fish, and also occurs in
Amphibia and Reptilia (the chameleon affording a well-known example).
Analogous powers exist in certain Crustacea and Cephalopoda. All these
rapid changes of colour are due to changes in shape or position of
superficial pigment cells controlled by the nervous system. That the
latter is itself stimulated by light through the medium of the eye and
optic nerve has been proved in many cases. Animals with a short
life-history passed in a single environment, which, however, may be very
different in the case of different individuals, may have a different
form of _variable cryptic colouring_, namely, the power of adapting
their colour once for all (many pupae), or once or twice (many larvae).
In these cases the effect appears to be produced through the nervous
system, although the stimulus of light probably acts on the skin and not
through the eyes. Particoloured surfaces do not produce particoloured
pupae, probably because the antagonistic stimuli neutralize each other
in the central nervous system, which then disposes the superficial
colours so that a neutral or intermediate effect is produced over the
whole surface (Poulton, _Trans. Ent. Soc. Lond._, 1892, p. 293). Cryptic
colouring may incidentally produce superficial resemblances between
animals; thus desert forms concealed in the same way may gain a likeness
to each other, and in the same way special resemblances, e.g. to lichen,
bark, grasses, pine-needles, &c., may sometimes lead to a tolerably
close similarity between the animals which are thus concealed. Such
likeness may be called _syncryptic_ or _common protective_ (or
_aggressive_) _resemblance_, and it is to be distinguished from mimicry
and common warning colours, in which the likeness is not incidental, but
an end in itself. Syncryptic resemblances have much in common with those
incidentally caused by functional adaptation, such as the mole-like
forms produced in the burrowing Insectivora, Rodentia and Marsupialia.
Such likeness may be called _syntechnic resemblance_