"The nature of their food has an important bearing upon the grouping of animals, and upon the extent of their distribution. Carnivorous animals are generally less con fined in their range than herbivorous ones, because their food is almost everywhere to be found/ The herbivora, on the other hand, are restricted to the more limited regions corresponding to the different zones of vegetation." Similarly, birds of prey, like the eagle and vtilture, have a much wider range than the granivorous and gallinaceous birds; but even the birds that wander furthest, have their definite limits; for example, the condor of the Cordilleras, although, from the extreme heights at which lie is often seen, he caniot fear a low temperature, is never found in the temperate region of the United States.
A very influential factor is the distribution of aquatic animals in the depths of water. The late prof. Forbes distinctly showed that we may recognize distinct faunas in zones of different depth, just as we mark different zones of animal and vegetable life in ascending lofty mountains. The zoophytes, molluscs, and even fishes, found near the shore in shallow water, usually differ very materially from those living at the depth of 20 or 30 ft.; and these, again, are different from those which are met with at a greater depth. The extreme depth at which animal life, in its lower forms, ceases to exist, is unknown; late researches, particularly the observations made in H.M.'s ships Porcupine
and Challenger, show that the region of animal life extends bathymetrically (to use prof. Forbes's word) much further than was formerly supposed, though beyond the depth of 6,000 ft. it gradually diminishes.
Before concluding these general remarks; we must observe that occasionally one or more animals are found in one very limited spot, and nowhere else; as, for example, the chamois and the ibex upon the Alps. (On this point, the reader should consult Dar win's of Researches, etc., in which it is shown that the Galapagos Archipelago, consisting of a small group of islands situated under the equator, and between 500 and 600 m. westward of the coast of America, not only contain numerous animals and plants that are found in no other part of the world, but that many of the species are exclu sively confined to a single island.) • All the faunas of the globe may be divided into three great groups, corresponding to the three great climatal divisions—viz., the arctic or glacial, the temperate, and the tropical faunas. while the two last-named faunas may be again divided into several zoological provinces. Each of these primary divisions demands a separate notice.