Mr. S. B. Wilson remarks: "Nature has shown great symmetry in regard to the species of this genus (Hemignathus including Heterorhynchus) to be found in the Sandwich Archipelago, three of the main islands having each a long-billed and a short-billed form." This, of course, is most natural. Both long-billed forms (Hemignathus) and short-billed forms (Heterorhynchus) have spread from the island where they were originally developed to the other islands, each changing as it is isolated from the main body of the species and subjected to natural selection under new conditions. With the genus Heterorhynchus, the forms with slender bills reach their culmina

tion.

Going back to the original stock, to which Oreomystis bairdi is perhaps the nearest living ally, we note first a divergence in another direction. In Rhodacanthis, the bill is stout like that of the large finch, not longer than the rest of the head, and curved downward a little at the tip. The species of this genus feed largely on the bean of the acacia and other similar trees, varying this with caterpillars and other insects. The stout bill serves to crush the seeds. In Chloridops, the bill is still heavier, very much like that of the grosbeak. Chloridops kona is, according to Mr. Robert Perkins, a dull, sluggish, solitary bird and very silent; its whole existence may be summed up in the words "to eat." Its food consists of the fruit of the aaka (bastard sandal tree), and as this is very minute, its whole time seems to be taken up in cracking the extremely hard shells of the fruit, for which its extraordinarily powerful bill and heavy head are well adapted.

"The incessant cracking of the fruits, when one of these birds is feeding, the noise of which can be heard for a considerable distance, renders the bird much easier to get than it otherwise would be. Its beak is always very dirty with a brown substance adhering to it which must be derived from the sandal nuts."

In Psittacirostra and Pseudonestor the bill suggests that of a parrot rather than that of a grosbeak. The mandibles are still very heavy, but the lower one, as in Heterorhynchus, is short and straight, while the much longer upper one is hooked over it. Pseudonestor feeds on the larvæ of wood-boring beetles (Clytanus) found in the koa trees (Acacia falcata), while the

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PLATE III.-1, Oreomystis bairdii Stejneger, Kauai; 2, Heterorhynchus olivaceus La Fresnaye, Hawaii. 3, Drepanis funerea Newton, Molokai. (From specimens.)

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closely related Psittacirostra eats only fruits, that of the ieie (Freycinetia arborea) and the red mulberry (Morus sapyrifera) being especially chosen. In all these genera, there is practically one species to each island, except that in some cases the species has not spread from the mountain or island in which we may suppose it to have been originally developed.

There are a few other song birds in the Hawaiian Islands, not related to the Drepanida. These are derived from the islands of Polynesia and have deviated from the original types in a degree corresponding to their isolation. In the case of the Drepanida, it seems necessary to conclude that natural selection is responsible for the physiological adaptations characteristic of the different genera. Such changes may be relatively rapid, and for the same reason they count for little from the standpoint of phylogeny. On the other hand, the nonuseful traits, the petty traits of form and coloration which distinguish a species in Oahu from its homologue in Kauai or Hawaii, are results of isolation. These results may be analyzed as in part differences in selection with different competition, different food and different conditions, and in part to hereditary difference due to the personal eccentricities in the parent stock from which the newer species was derived.

In these as in all similar cases we may confidently affirm: the adaptive characters a species may present are due to natural selection or are developed in connection with the demands of competition. The characters nonadaptive which chiefly distinguish species do not result from natural selection, but are connected with some form of geographical isolation and the segregation of individuals resulting from it.

The origin of races and breeds of domestic animals is in general of much the same nature. In traveling over England one is struck by the fact that each county has its own breed of sheep, each of these having its type of excellence in mutton, wool, hardiness, or fertility, but the breeds distinguished by characters having no utility either to sheep or to

The breeds are formed primarily by isolation. The traits of the first individuals in each region are intensified by the inbreeding resulting from segregation. Natural selection preserves the hardiest, the most docile, and the most fertile: artificial selection those which yield the most wool, the best mutton and the like. The breed once established, artificial

selection also tends to intensify and to preserve its nonadaptive characteristic marks. The more pride the breeders take in their stock, the more certain is the preservation of the breed's useless peculiarities. Very few of the characters which usually distinguish a breed of domestic animals have the slightest physiological value to the species. Each of them would disappear in a few generations of crossing, and in each race prized by the breeder the actual virtues exist wholly independently of these race marks.

Analogous to the race peculiarities of domestic animals are the minor traits among the men of different regions. Certain gradual changes in speech are due to adaptation, the fitness of the word for its purpose, analogous to natural selection. The nonadaptive matters of dialect find their origin in the exigencies of isolation, while languages in general are explainable by the combined facts of migration, isolation, and the adaptation of words for the direct uses of speech.

In the animal kingdom generally we may say therefore: Whenever a barrier is to some extent traversable, the forms separated by it are likely to cross from one side to the other, thus producing intergradations, or forms more or less intermediate between the one and the other. For every subspecies, where the nature of the variation has been carefully studied, there is always a geographical basis. This basis is defined by the presence of some sort of physical barrier. It is extremely rare to find two subspecies inhabiting or breeding in exactly the same region. When such appears to be the case, there is really some difference in habit or in habitat: the one form lives on the hills, the other in the valleys; the one feeds on one plant, the other on another; the one lives in deep water, the other along the shore. There can be no possible doubt that subspecies are nascent species, and that the accident of intergradation in the one case and not in the other implies no real difference in origins.

For a final example, we may compare the species of American orioles constituting the genus Icterus. We may omit from consideration the various subspecies, set off by the mountain chains, and the usual assemblage of insular forms, one in each of the West Indies, and confine our attention to the leading species as represented in the United States. (See frontispiece.)