and swimmers. Of the fourteen families of the former groups, four are quite and one nearly cosmopolitan; and of the eight families of the latter group, among which are some powerful fliers, only three have not a universal diffusion; and the two groups exhibit more genera occurring over nearly the whole earth (eighteen out of ninety-six and eleven out of seventy-nine) than all the other families of birds put together. But we can not overlook the fact that some of these genera stand on a very feeble footing.
It is interesting to observe that, in the other orders of birds, those kinds that live on fish are very widely spread. Thus, the kingfishers are cosmopolitan, and the genus Ceryle, which Brehm says includes "the strongest, most active, and most ravenous members of the family," is especially wide-spread, and is without representatives only in Australia, Madagascar, Europe, and Xorthern Asia. The nine not greatly differing species of water-ousel, whose habits are much like those of the true kingfishers, are very widely diffused wherever there are cool, clear, and rapid mountain-brooks.
The distribution is less wide of such birds as live principally on land-invertebrates, especially on articulates. Their occurrence is largely dependent, like that of plant-feeders, indirectly but intimately on the character of the vegetation; and those forms among them which, like titmice, wrens, and woodpeckers, live on insects at rest, as well as on eggs and pupæ, or on larvæ, either concealed or living in wood, and changing place but little, have the most extensive range; and, since larvæ pass the winter in one of the forms mentioned, they are permanent residents in temperate climates. In the measure that a bird pursues perfect insects, particularly those which fly, it becomes possible for it to be an established inhabitant only in warm climates. To dwell in colder regions, if it usually refuses vegetable food, it must be a good flier, and is then compelled to go away on the approach of the cold season and the accompanying disappearance of its food.
The presence of plant-eating birds is still more predominantly dependent on their food; and it is a matter of interest to observe how the opening out of the vegetation of a country reacts upon its ornithic population. Africa, wherever it is not wooded or desert, the Europeo-Asiatic steppes, and the prairies of America, are covered with grass and other mealy-seeded herbs, and are also the dwelling-places of hosts of weaver-birds, larks, and other grain-eaters, the flocks of whose numerous species are numbered by the thousand; and wherever they can find their food in winter, they abide. Groups of berry-bearing plants cover extensive regions of the north, and follow, as they stretch down toward the south, the cooler regions of the higher mountains; and in their suite we find everywhere, in the tundras of Siberia, on the slopes of the Himalayas, and in the Peruvian Andes, fruit-eating birds of similar genera. In the fruit-rich woods of the tropics, especially of South America, more than half of the native birds, though represent-
