. Atlas of zoogeography; a series of maps illustrating the distribution of over seven hundred families, genera, and species of existing animals. Zoology; Zoogeography. GENERAL PRINCIPLES OF DISTRIBUTION nearest land. From the direction of the wind during the four days previous to the occurrence, it appeared to be beyond doubt that the insects had come from the islands named, and must therefore have crossed nearly a thousand miles of ocean! Large numbers of insects lay their eggs in timber, and hence the agency of floating logs in aiding dispersal must be taken into account, especially as such
. Atlas of zoogeography; a series of maps illustrating the distribution of over seven hundred families, genera, and species of existing animals. Zoology; Zoogeography. GENERAL PRINCIPLES OF DISTRIBUTION nearest land. From the direction of the wind during the four days previous to the occurrence, it appeared to be beyond doubt that the insects had come from the islands named, and must therefore have crossed nearly a thousand miles of ocean! Large numbers of insects lay their eggs in timber, and hence the agency of floating logs in aiding dispersal must be taken into account, especially as such creatures in the egg-state may retain their vitality for a considerable time. Marine animals live under more uniform conditions than those on the land, but their means of dispersal may be briefly touched upon. Mammals, such as Seals and Walruses, sometimes undertake long sea journeys, -while the wanderings of the huge Cetaceans seem only to be limited by considera- tions of temperature. The same remark applies largely to fishes, but with them the depth of water may also have its influence on their dispersal. Fresh-water fishes may travel from one large river-system to another when the sources of the streams are near enough to each other, and through changes in land-level the direction of streams may be altered, and lead to considerable corresponding changes in the fauna. Lastly, the eggs of fishes may be, and no doubt often are, carried from one district to another by aquatic birds. CONDITIONS LIMITING DISPERSAL. Against the various phenomena favouring dispersal which have been noticed above, must be reckoned certain factors which act in the way of species to a varying degree of heat and cold, and on the whole it may be said that temperature does indeed play a not unimportant part in determining or limiting the range of animals. It may be added, that the closest depend- ence in this respect upon temperature is to be found ainong marine organisms. Indeed, this is often the only
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Keywords: ., bookauthorcl, bookcentury1900, bookdecade1910, booksubjectzoology
