Page:EB1911 - Volume 13.djvu/724

Rh and cellular structure found in the others. So dense and hard is this portion of the “helmet” that Chinese and Malay artists carve figures on its surface, or cut it transversely into plates, which from their agreeable colouring, bright yellow with a scarlet rim, are worn as brooches or other ornaments. This bird, which is larger than a raven, is also remarkable for its long graduated tail, having the middle two feathers nearly twice the length of the rest. Nothing is known of its habits. Its head was figured by George Edwards in the 18th century, but little else had been seen of it until 1801, when John Latham described the plumage from a specimen in the British Museum, and the first figure of the whole bird, from an example in the Museum at Calcutta, was published by General Hardwicke in 1823 (Trans. Linn. Society, xiv. pl. 23). Yet more than twenty years elapsed before French naturalists became acquainted with it.

In the Bucorvinae we have only the genus Bucorvus, or Bucorax as some call it, confined to Africa, and containing at least two and perhaps more species, distinguishable by their longer legs and shorter toes, the ground-hornbills of English writers, in contrast to the Bucerotinae which are chiefly arboreal in their habits, and when not flying move by short leaps or hops, while the members of this group walk and run with facility. From the days of James Bruce at least there are few African travellers who have not met with and in their narratives more or less fully described one or other of these birds, whose large size and fearless habits render them conspicuous objects.

As a whole the hornbills, of which more than 50 species have been described, form a very natural and in some respects an isolated group, placed by Huxley among his Coccygomorphae. It has been suggested that they have some affinity with the hoopoes (Upupidae), and this view is now generally accepted. Their supposed alliance to the toucans (Rhamphastidae) rests only on the apparent similarity presented by the enormous beak, and is contradicted by important structural characters. In many of their habits, so far as these are known, all hornbills seem to be much alike, and though the modification in the form of the beak, and the presence or absence of the extraordinary excrescence, whence their name is derived, causes great diversity of aspect among them, the possession of prominent eyelashes (not a common feature in birds) produces a uniformity of expression which makes it impossible to mistake any member of the family. Hornbills are social birds, keeping in companies, not to say flocks, and living chiefly on fruits and seeds; but the bigger species also capture and devour a large number of snakes, while the smaller are great destroyers of insects. The older writers say that they eat carrion, but further evidence to that effect is required before the statement can be believed. Almost every morsel of food that is picked up is tossed into the air, and then caught in the bill before it is swallowed. They breed in holes of trees, laying large white eggs, and when the hen begins to sit the cock plasters up the entrance with mud or clay, leaving only a small window through which she receives the food he brings her during her incarceration.

This remarkable habit, almost simultaneously noticed by Dr Mason in Burma, S. R. Tickell in India, and Livingstone in Africa, and since confirmed by other observers, especially A. R. Wallace in the Malay Archipelago, has been connected by A. D. Bartlett (Proc. Zool. Society, 1869, p. 142) with a peculiarity as remarkable, which he was the first to notice. This is the fact that hornbills at intervals of time, whether periodical or irregular is not yet known, cast the epithelial layer of their gizzard, that layer being formed by a secretion derived from the glands of the proventriculus or some other upper part of the alimentary canal. The epithelium is ejected in the form of a sack or bag, the mouth of which is closely folded, and is filled with the fruit that the bird has been eating. The announcement of a circumstance so extraordinary naturally caused some hesitation in its acceptance, but the essential truth of Bartlett’s observations was abundantly confirmed by Sir W. H. Flower and especially by Dr J. Murie. These castings form the hen bird’s food during her confinement.

HORNBLENDE, an important member of the amphibole group of rock-forming minerals. The name is an old one of German origin, and was used for any dark-coloured prismatic crystals from which metals could not be extracted. It is now applied to the dark-coloured aluminous members of the monoclinic amphiboles, occupying in this group the same position that augite occupies in the pyroxene group. The monoclinic crystals are prismatic in habit with a six-sided cross-section; the angle between the prism-faces (M), parallel to which there are perfect cleavages, is 55° 49′. The colour (green, brown or black) and the specific gravity (3.0-3.3) vary with the amount of iron present. The pleochroism is always strong, and the angle of optical extinction on the plane of symmetry (x in the figure) varies from 0° to 37°. The chemical composition is expressed by mixtures in varying proportions of the molecules Ca(Mg, Fe)3(SiO3)4, (Mg, Fe)(Al, Fe)2SiO6 and NaAl(SiO3)2. Numerous varieties have been distinguished by special names: edenite, from Edenville in New York, is a pale-coloured aluminous amphibole containing little iron; pargasite, from Pargas near Abo in Finland, a green or bluish-green variety; common hornblende includes the greenish-black and black kinds containing more iron. The dark-coloured porphyritic crystals of basalts are known as basaltic hornblende.

Hornblende occurs as an essential constituent of many kinds