358 H U M M I -N G-B I R D together with, the Goatsuckers (Caprimulgidce), to form the division Cypselomorphce one of the two into which he has separated his larger group ^Egithognathae, However, the most noticeable portion of the Humming-bird s skeleton is the sternum, which in proportion to the size of the bird is enormously developed both longitudinally and vertically, its deep keel and posterior protraction affording abundant space for the powerful muscles which drive the wings in their rapid vibrations as the little creature poises itself over the flowers where it finds its food. 1 So far as is known, all Humming-birds possess a protru- sible tongue, in conformation peculiar among the class Aves, though to some extent similar to that member in the Woodpeckers (Picidce) 2 the "horns" of the hyoid apparatus upon which it is seated being greatly elongated, passing round and over the back part of the head, near the top of which they meet, and thence proceed forward, lodged in a broad and deep groove, till they terminate in front of the eyes. But, unlike the tongue of the Woodpeckers, that of the Humming-birds consists of two cylindrical tubes, tapering towards the point, and forming two sheaths which contain the extensile portion, and are capable of separation, thereby facilitating the extraction of honey from the nectaries of flowers, and with it, what is of far greater importance for the bird s sustenance, the small insects that have been attracted to feed upon the honey. 3 These, on the tongue being withdrawn into the bill, are caught by the mandibles (furnished in the males of many species with fine, horny, saw- like teeth 4 ), and swallowed in the usual way. The stomach is small, moderately muscular, and with the inner coat slightly hardened. There seem to be no caeca. The trachea is remarkably short, the bronchi beginning high up on the throat, and song-muscles are wholly wanting, as in all other Cypselomorplioe. 5 Humming-birds, as is well known, comprehend the smallest members of the class Aves. The largest among them measures no more than 8 inches and a half, 6 and the least 2 inches and three-eighths in length, for it is now admitted generally that Sloane must have been in error when he de scribed ( Voyage, ii. p. 308) the " Least Humming-bird of Jamaica" as "about inch long from the end of the bill to that of the tail" unless, indeed, he meant the proximal end of each, an interpretation, however, that will not save Edwards and Latham from the charge of careless misstatement, when they declare that they had received such a bird from that island. Next to their generally small size, the best known characteristic of the Trochilidce is the wonderful brilliancy of the plumage of nearly all their forms, in which respect 1 This is especially the case with the smaller species of the group, for the larger, though shooting with equal celerity from place to place, seem to flap their wings with comparatively slow but not less powerful strokes. The difference was especially observed with re spect to the largest of all Humming-birds, Patagona gigas, by Mr Darwin. 2 The resemblance, so far as it exists, must be merely the result of analogical function, and certainly indicates no affinity between the families. 3 It is probable that in various members of the Trochilidce the struc ture of the tongue, and other parts correlated therewith, will be found subject to several and perhaps considerable modifications, as is the case in various members of the Picidce. At present there are scarcely half a dozen species of Humming-birds of which it can be said that any part of their anatomy is known. 4 These are especially observable in Rhamphodon ncevius and An- drodon cequatorialis. B t Mr Gosse (Birds of Jamaica, p. 130) says that Mellisuga minima, the smallest species of the Family, has "a real song " but the like is not recorded of any other. 6 There are several species in which the tail is very much elongated, such as the well-known Aithurus polytmus of Jamaica, and the re markable Loddigesia mirabilis of Chachapoyas in Peru, which last was until lately only known from a unique specimen (Ibis, 1880, p. 152) ; but " trochilidists in giving their measurements do not take these extraordinary developments into account. they are surpassed by no other birds, and are only equalled by a few, as, for instance, by the Nectar iniidce, or Sun- birds of the tropical parts of the Old World, in popular estimation so often confounded with them, and even by some mistaken naturalists thought to be their allies. The number of species of Humming-birds now known to exist considerably exceeds 400 ; and, though none depart very widely from what a morphologist would deem the typical structure of the Family, the amount of modification, within certain limits, presented by the various forms is surprising and even bewildering to the un initiated. But the features that are ordinarily chosen by systematic ornithologists in drawing up their schemes of classification are found by the " trochilidists," or special students of the Trochilidce, insuf ficient for the purpose of arranging these birds in groups, and char acters on which genera can be founded have to be sought in the style and coloration of plumage, as well as in the form and propor tions of those parts which are most generally deemed sufficient to furnish them. Looking to the large number of species to be taken into account, convenience has demanded what science would with hold, and the genera established by the ornithologists of a preced ing generation have been broken up by their successors into multi tudinous sections the more adventurous making from 150 to 180 of such groups, the modest being content with 120 or thereabouts, but the last dignifying each of them by the title of genus. It is of course obvious that these small divisions cannot be here considered in detail, nor would much advantage accrue by giving statistics from the works of the latest trochilidists, Messrs Gould, 7 Mulsant, 8 and Elliot. 9 It would be as unprofitable here to trace the successive steps by which the original genus Trochilus of Liumeus, or the two genera Polytmus and Mellisuga of Brisson, have been split into others, or have been added to, by modern writers, for not one of these professes to have arrived at any final, but only a provisional, arrange ment ; it seems, however, expedient to notice the fact that some of the authors of the last century 10 supposed themselves to have seen the way to dividing what we now know as the Family Trochilidce into two groups, the distinction between which was that in the one the bill was arched and in the other straight, since that difference has been insisted on in many works. This was especially the view taken by Brisson and Buffbn, who termed the birds having the arched bill " Colibris," and those having it straight " Oiscaux-mouchcs." The distinction wholly breaks down, not merely because there are Trochilidce which possess almost every gradation of decurvatibn of the bill, but some which have the bill upturned after the manner of that strange bird the Avocet, 11 while it may be remarked that several of the species placed by those authorities among the " Coli- bris" are not Humming-birds at all. The extraordinarily brilliant plumage which most of the Trochi lidce exhibit has been already mentioned, and in describing it orni thologists have been compelled to adopt the vocabulary of the jeweller in order to give an idea of the indescribable radiance that so often breaks forth from some part or other of the investments of these feathered gems. In all save a few of other birds, the most imaginative writer sees gleams which lie may adequately designate metallic, from their resemblance to burnished gold, bronze, copper, or steel, but such similitudes wholly fail when he has to do with the Trochilidce, and there is hardly a precious stone ruby, amethyst, sapphire, emerald, or topaz the name of which may not fitly, and without any exaggeration, be employed in regard to Humming-birds. In some cases this radiance beams from the brow, in some it glows from the throat, in others it shines from the tail-coverts, in others it sparkles from the tip only of elongated feathers that crest the head or surround the neck as with a frill, while again in others it may appear as a luminous streak across the cheek or auriculars. The feathers that cover the upper parts of the body very frequently have a metallic lustre of golden-green, which in other birds would be thought sufficiently beautiful, but in the Trochilidce its sheen is overpowered by the almost dazzling splendour that radiates from the spots where Nature s lapidary has set her jewels. The flight feathers are almost invariably dusky the rapidity of their movement would, perhaps, render any display of colour ineffective ; while, on the con trary, the feathers of the tail, which, as the bird hovers over its food- bearing flowers, is almost always expanded, and is therefore compara tively motionless, often exhibit arichtranslucency, as of stainedglasp, but iridescent in a manner that no stained glass ever is cinnamon merging into crimson, crimson changing to purple, purple to violet, 7 A Monograph of the Trochilidce or Humming-birds, 5 vols. imp. fol., London, 1861 (with Introduction in 8vo). 8 Histoire naturelle des Oiseaucc-M ouches ou Colibris, 4 vols. with supplement, imp. 4to, Lyon-Geneve-Bale, 1874-77. a Smithsonian Contributions to Knowledge, No. 317,^4 Classification and Synopsis of the Trochilidce, 1 vol. imp. 4to, Washington, 1879. 10 Salerne must be. excepted, especially as he was rebuked by Butfon for doing what we now deem right. 11 For example Avocettula recurvirostris of Guiana and A.euryptera
of Colombia.
