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Show AN OTATIONS AND ADDITIONS. 303 ment, and the whole vital process; to all this must be further added hygrometric influences and those of atmospheric electricity. My inve tigations respecting the numerical laws of the distribution of forms may possibly be applied at some future day with advantage to the different classes of Rotiferre in the animal creation. The rich collections at the l\'Iuseum d'Histoire Naturelle in the Jardin de Plantes at Paris, already contained, in l820 (according to approximate estimations), above 56,000 phrenogamous and cryptogamous plants in herbariums, 44:,000 insects (a number doubtless too small, though given me by Latreille), 2500 species of fish, 700 reptile , 4000 birds, and 500 mammalia. Europe has about 80 species of indigenous mammalia, 400 birds, and 30 reptiles. In the Northern temperate zone, therefore, the species of birds are five times more numerous than those of mammalia, as there are in Europe five times as many Compositre as there are Amentacere and Coniferre, and five times as many Leguminosre as there are Orehidere and Euphorbiacre. In the southern hemisphere, the ratio of mammalia is in tolerably striking agreement, being as 1 to 4.3. Birds, and still more reptiles, increase in the number of species, in approaching the torrid zone, more than the mammalia. Cuvier's researches might lead us to believe that the proportion was different in the earlier state of things, and that many more ma~malia had perished by revolutions of Nature than birds. Latreille has shown what groups of insects increase towards the Pole, and what towards the Equator. Illiger has given the countries of 3800 species of birds according to the quarters of the globe: it would have been much more instructive if the same thing had been done according to zones. We should find little difficulty in comprehending how, on a given space of the earth's surface, the individuals of a class of plants or animals limit each other's numbers, or how, after long-continued contest and many fluctuations caused by the requirements of nourishment and mode of life, a state of equilibrium should be at last established; but the causes which have limited not the number of individuals of a form but the forms themselves, in a particular space, and founded their typical diversity, are placed beneath the impenetrable veil which still conceals from our eyes all that relates to the manner of the first creation and commencement of organic beings. |