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Page:Littell's Living Age - Volume 134.djvu/317

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THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

naturalist, accustomed to the comparative abundance of insect life, even in the south of England, more than its usual scantiness in Ireland, although the latter country probably possesses about two-thirds of our English species.

The Mediterranean subregion presents us with several interesting problems, in addition to some previously mentioned. During the time that Spain and Italy have been separated from north Africa, great changes have occurred in the insects of the opposite coasts, as well as in the larger animals which now inhabit those countries. Oberthur, in his recently published work on the lepidoptera of Algeria, doubts if any Algerian species of Zygæna is identical with any European species. This, however, might perhaps be expected, for the genus Zygæna consists of a great number of closely allied and highly variable species which have their headquarters in the Mediterranean subregion; and while some groups of animals (as many mollusca) may remain almost unchanged for entire geological periods, yet others, which, like the species of Zygæna, are specifically unstable, may become modified very rapidly. But, notwithstanding the large amount of speciality in the Algerian insect fauna, it is essentially the same as the European, and the African element is exceedingly small. (There are some species of insects confined to south Spain and south Russia. These are probably very ancient forms, and may even be relics of the pre-glacial Palæarctic insect-fauna.) The large mammals of Algeria are apparently nearly all of African origin, having crossed from the south after the glacial epoch, and subsequently to the disappearance of the Saharan sea, and to the final separation of Europe and Africa, although some identical species of wide range penetrated into, or perhaps returned to Europe through Asia Minor, such, for instance, as the lion.

The Ethiopian region, or Africa, is at the present day chiefly remarkable for the great number of large mammalia which inhabit it. Many of these, though formerly abundant in Europe and India, have long disappeared from both countries; and Africa has now a highly specialized character of its own. The Malagasy sub-region, including Madagascar and the adjacent islands, is peculiarly remarkable, and appears to indicate a very ancient connection with the southern portion of Africa, before the apes, ungulates, and felines had entered it." (Wallace, " Geogr. Distr." I, p. 273.) The insects of Madagascar, however, are closely allied to existing African species, and many of the most remarkable, formerly supposed to be peculiar to the island, have since been received from Natal or Zanzibar. There is also a considerable resemblance between the Mascarene fauna, and that of distant parts of the world, in which connection we may refer to the numerous traditions, previously mentioned, of recent subsidences in various parts of the Indian Ocean.

As a rule, competition is far more severe on continents than on islands; hence the great number of peculiar forms which survive in islands, though long superseded on continents, and it appears that according to this principle, the insects of Madagascar have become less strongly modified than those of the African continent, and therefore represent to some extent a more ancient fauna. A remarkable case is afforded by two pairs of butterflies, inhabiting different parts of the world. One is Papilis Merope, a large black-and-white butterfly, with tails on the hind wings, found all over tropical Africa, and varying considerably in different localities. The females are altogether unlike the male, being without a tail, and of a totally different shape and color, resembling butterflies of other groups, which are protected from birds, etc., by their nauseous odor. But P. Merope is represented in Madagascar by P. Meriones, the female of which only differs from the male in the presence of an additional black bar on the fore wings. The other example is that of Argynnis Niphe, a common Indian species, which is tawny, with black spots, and the female of which has the tips of the fore wings broadly dusky, with a black bar across them, giving it a great resemblance to Danaus Chrysiphus, a widely distributed insect, which is "mimicked" in the same way by the females of several other butterflies besides A. Niphe, even including one of the female varieties of Papilio Merope, already referred to. But the Australian representative of A. Niphe (A. inconstans), though differing so little from the male of A. Niphe that it was long considered to be no more than a slight local variety, has the sexes alike, the female having no white bar on the wings, although a small Danaus (D. petilia) closely allied to D. Chrysippus, is also found in Australia.

Turning to the Oriental region, we find that north India is much richer in species than the south. This is partly owing to the greater variety of elevation (just as the southern peninsulas of Europe are poorer