ittle and cannot be renewed. The eyeballs are large, but the lids are
united into one concentric fold, leaving only the small pupil visible.
The right and left eyes are incessantly moved separately from each other
and literally in every direction, up and down, forwards and straight
backwards, producing the most terrible squinting. Chameleons alone of
all reptiles can focus their eyes upon one spot, and conformably they
alone possess a retinal _macula centralis_, or spot of acutest,
binocular vision. The tongue has attained an extraordinary development.
It is club-shaped, covered with a sticky secretion, and based upon a
very narrow root, which is composed of extremely elastic fibres and
telescoped over the much elongated, style-shaped, copular piece of the
hyoid. The whole apparatus is kept in a contracted state like a spring
in a tube. When the spring is released, so to speak, by filling the
apparatus with blood and by the play of the hyoid muscles, the heavy
thick end shoots out upon the insect prey and is withdrawn by its own
elasticity. The whole act is like a flash. An ordinary chameleon can
shoot a fly at the distance of fully 6 in., and it can manage even a big
sphinx moth.

[Illustration: Left Forefoot of _Chamaeleon o'shaughenesii_, outer
view.]

Another remarkable feature is their changing of colour. This proverbial
power is greatly exaggerated. They cannot assume in succession all the
colours of the rainbow, nor are the changes quick. The common chameleon
may be said to be greenish grey, changing to grass-green or to dull
black, with or without maroon red, or brown, lateral series of patches.
At night the same specimen assumes as a rule a more or less uniform pale
straw-colour. After it has been watched for several months, when all its
possibilities seem exhausted, it will probably surprise us by a totally
new combination, for instance, a black garb with many small yellow
specks, or green with many black specks. Pure red and blue are not in
the register of this species, but they are rather the rule upon the dark
green ground colour of the South African dwarf chameleon. The changes
are partly under control of the will, partly complicated reflex actions,
intentionally adaptive to the physical and psychical surroundings. The
mechanism is as follows. The cutis contains several kinds of specialized
cells in many layers, each filled with minute granules of guanine. The
upper cells are the smallest, most densely fi