s as if to strike a foe.[112]
Dr. A.B. Meyer has also discovered that, while some species of the genus
Callophis (belonging to the same family as the American Elaps) have
large poison fangs, other species of the same genus have none; and that
one of the latter (C. gracilis) resembles a poisonous species (C.
intestinalis) so closely, that only an exact comparison will discover
the difference of colour and marking. A similar kind of resemblance is
said to exist between another harmless snake, Megaerophis flaviceps, and
the poisonous Callophis bivirgatus; and in both these cases the harmless
snake is less abundant than the poisonous one, as occurs in all examples
of true mimicry.[113]

In the genus Elaps, above referred to, the very peculiar style of colour
and marking is evidently a "warning colour" for the purpose of
indicating to snake-eating birds and mammals that these species are
poisonous; and this throws light on the long-disputed question of the
use of the rattle of the rattlesnake. This reptile is really both
sluggish and timid, and is very easily captured by those who know its
habits. If gently tapped on the head with a stick, it will coil itself
up and lie still, only raising its tail and rattling. It may then be
easily caught. This shows that the rattle is a warning to its enemies
that it is dangerous to proceed to extremities; and the creature has
probably acquired this structure and habit because it frequents open or
rocky districts where protective colour is needful to save it from being
pounced upon by buzzards or other snake-eaters. Quite parallel in
function is the expanded hood of the Indian cobra, a poisonous snake
which belongs also to the Elapidae. This is, no doubt, a warning to its
foes, not an attempt to terrify its prey; and the hood has been
acquired, as in the case of the rattlesnake, because, protective
coloration being on the whole useful, some mark was required to
distinguish it from other protectively coloured, but harmless, snakes.
Both these species feed on active creatures capable of escaping if their
enemy were visible at a moderate distance.

_Mimicry among Birds._

The varied forms and habits of birds do not favour the production among
them of the phenomena of warning colours or of mimicry; and the extreme
development of their instincts and reasoning powers, as well as their
activity and their power of flight, usually afford them other means of
evading their enemies. Yet there ar