and ibises. In legs, feet and tails, there are corresponding
differences. There are tails of all lengths and all forms; soft and
stiff, square, acuminated, broad and fan-like, narrow and spine-like,
and many as in the woodpeckers, and used as in that bird to support the
body in climbing. An extremely curious modification is found in
Sittosoma: the tail-feathers in this genus are long and graduated, and
the shafts, projecting beyond the webs at the ends, curve downwards and
form stiff hooks. Concerning the habits of these birds, it has only been
reported that they climb on the trunks of trees: probably they are able
to run vertically up or down with equal facility, and even to suspend
themselves by their feather-hooks when engaged in dislodging insects.
Another curious variation is found in Sylviothorhynchus, a small
wren-like bird and the only member known of the genus, with a tail
resembling that of the lyre-bird, the extravagantly long feathers being
so narrow as to appear almost like shafts destitute of webs. This tail
appears to be purely ornamental.

This extreme variety in structure indicates a corresponding diversity in
habits; and, assuming it to be a true doctrine that habits vary first
and structure afterwards, anyone might infer from a study of their forms
alone that these birds possess a singular plasticity, or tendency to
vary, in their habits--or, in other words, that they are exceptionally
intelligent; and that such a conclusion would be right I believe a study
of their habits will serve to show.

The same species is often found to differ in its manner of life in
different localities. Some species of Xenops and Magarornis, like
woodpeckers, climb vertically on tree-trunks in search of insect prey,
but also, like tits, explore the smaller twigs and foliage at the
extremity of the branches; so that the whole tree, from its root to its