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skill certain well recognized principles, construct what may fairly be tern ed a 

 natural system. 



In sixch a system groups of species are collected into genera, gi-oups of genera 

 into orders, and groups of orders into classes ; each order comprising a number 

 of genera distinct from those of the others, but which, nevertheless, are distin- 

 guished by certain general characters different from those of any other orders 

 of plants, characters, too, which are preserved through every existing 

 modification of form. 



I have thus shown you that the organic world is primarily divided into 

 two great kingdoms ; that each of these is subdivided into classes, orders, 

 genera, and so-called species ; and that every species is held to possess two 

 leading tendencies, the one to vary, and the other to accumulate such variations 

 where profitable, by transmitting to its descendants the modifications resulting 

 from variation. I now purpose, in the next place, to call your attention shortly 

 to certain observed facts in relation to the geographical distribution of animals 

 and plants. 



The Abbe Domenech has observed that "if Eden were the birthplace 

 of mankind, it certainly was not the birthplace of the whole animal and 

 vegetable creation, for," he says, "the works of God invariably bear the witness 

 of Divine Wisdom, and to have created in Eden the Reindeer of Lapland, 

 the Lama of Peru, the Kangaroo of Australia, and the Ostrich of the Sahara, 

 would have been as useless as to people the coasts of Tyre and Sidon with 

 the Whale of Greenland, the Tortoise of the Gulf of Mexico, and with fishes 

 which only live in Intertropical and Hyperborean regions." 



" In considering the distribution of organic life over +he globe," says Mr. 

 Darwin, " the first great fact which strikes us is, that neither the similarity 

 nor the dissimilarity of the inhabitants of various regions can be accounted for 

 by their climatal and other physical conditions. Of late, almost every author 

 who has studied the subject, has come to this conclusion. The case of America 

 alone would suffice to prove its truth ; for, if we exclude the northern parts 

 where the circumpolar land is almost continuous, all authors agree that one of 

 the most fundamental divisions in geographical distribution is that between 

 the New and Old Worlds ; yet if we travel over the vast American Continent, 

 from the central parts of the United States to its extreme southern point, we 

 meet with most diversified conditions ; the most humid districts, arid deserts, 

 lofty mountains, grassy plains, forests, marshes, lakes, and great rivers, under 

 almost every temperature. There is hardly a climate or condition in the Old 

 World which cannot be paralleled in the New, at least as closely as the same 

 species generally require ; for it is a most rare case to find a group of organisms 

 confined to any small spot, having conditions peculiar in only a slight degree j 

 for instance, small areas in the Old World could be pointed out hotter than 

 any in the New World, yet these are not inhabited by a peculiar fauna or 

 flora. Notwithstandsng this parallelism in the conditions of the Old and New 

 Worlds, how widely different are their living productions ! 



" In the Southern Hemisphere, if we compare large tracts of land in 

 Australia, South Africa, and Western South America, between latitudes 25° 

 and 35°, we shall find parts extremely similar in all their conditions; yet it 

 would not be possible to point out thi-ee faunas and floras more utterly 

 dissimilar. Or again, we may compare the productions of South America, 

 south of lati tude 35° with those north of 25°, which consequently inhabit a 

 considerably different climate, and they will be found incomparably more 

 closely related to each other, than they are to the productions of Australia or 

 Africa under nearly the same climate. Analagous facts could be given with 

 respect to the inhabitants of the sea." 



The author from whom I have just quoted, then points to certain facts 



