mes see individuals following habits different from those
proper to their species and to the other species of the same genus, we
might expect that such individuals would occasionally give rise to
new species, having anomalous habits, and with their structure either
slightly or considerably modified from that of their type. And such
instances occur in nature. Can a more striking instance of adaptation be
given than that of a woodpecker for climbing trees and seizing insects
in the chinks of the bark? Yet in North America there are woodpeckers
which feed largely on fruit, and others with elongated wings which chase
insects on the wing. On the plains of La Plata, where hardly a tree
grows, there is a woodpecker (Colaptes campestris) which has two toes
before and two behind, a long-pointed tongue, pointed tail-feathers,
sufficiently stiff to support the bird in a vertical position on a post,
but not so stiff as in the typical wood-peckers, and a straight, strong
beak. The beak, however, is not so straight or so strong as in the
typical woodpeckers but it is strong enough to bore into wood. Hence
this Colaptes, in all the essential parts of its structure, is a
woodpecker. Even in such trifling characters as the colouring, the harsh
tone of the voice, and undulatory flight, its close blood-relationship
to our common woodpecker is plainly declared; yet, as I can assert, not
only from my own observations, but from those of the accurate Azara, in
certain large districts it does not climb trees, and it makes its
nest in holes in banks! In certain other districts, however, this same
woodpecker, as Mr. Hudson states, frequents trees, and bores holes in
the trunk for its nest. I may mention as another illustration of the
varied habits of this genus, that a Mexican Colaptes has been described
by De Saussure as boring holes into hard wood in order to lay up a store
of acorns.

Petrels are the most aerial and oceanic of birds, but, in the quiet
sounds of Tierra del Fuego, the Puffinuria berardi, in its general
habits, in its astonishing power of diving, in its manner of swimming
and of flying when made to take flight, would be mistaken by any one for
an auk or a grebe; nevertheless, it is essentially a petrel, but with
many parts of its organisation profoundly modified in relation to its
new habits of life; whereas the woodpecker of La Plata has had its
structure only slightly modified. In the case of the water-ouzel, the
acutest obser