It is strange to find a Passerine family, numerous as the Tree-creepers, uniformly of one colour, or nearly so; for, with few exceptions, these birds have a brown plumage, without a particle of bright colour. But although they possess no brilliant or metallic tints, in some species, as we shall see, there are tints approaching to brightness. Notwithstanding this family likeness in colour, any person, not an ornithologist, looking at a collection of specimens comprising many genera, would hear with surprise and almost incredulity that they all belonged to one family, so great is the diversity exhibited in their structure. In size they vary from species smaller than the golden-crested wren to others larger than the woodcock; but the differences in size are as nothing compared with those shown in the form of the beak. Between the minute, straight, conical, tit-like beaks of the Laptasthenura--a tit in appearance and habits--and the extravagantly long, sword-shaped bill of Nasica, or the excessively attenuated, sickle-shaped organ in Xiphorynchus, the divergence is amazing, compared with what is found in other families; while between these two extremes there is a heterogeneous assemblage of birds with beaks like creepers, nuthatches, finches, tyrant-birds, woodpeckers, crows, and even curlews 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.