The Descent of Man

that they serve the same general purpose in the
economy of these two animals. The first conjecture,
which will occur to every one, is that they
are used by the males for fighting together; and
as these animals are very quarrelsome (69. Dr.
Buchholz, 'Monatsbericht K. Preuss. Akad.' Jan.
1874, p. 78.), this is probably a correct view. Mr.
T.W. Wood also informs me that he once watched
two individuals of C. pumilus fighting
violently on the branch of a tree; they flung
their heads about and tried to bite each other;
they then rested for a time and afterwards continued
their battle.
With many lizards the sexes differ slightly in
colour, the tints and stripes of the males being
brighter and more distinctly defined than in the
females. This, for instance, is the case with the
above Cophotis and with the Acanthodactylus
capensis of S. Africa. In a Cordylus of the latter
country, the male is either much redder or greener
than the female. In the Indian Calotes nigri-