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332 ANNUAL OF SCIENTIFIC DISCOVERY. 



vegetation at those points. In proportion as we pass south, the Old 

 and New Worlds become more and more unlike, while the great 

 continent of Australia, lying off, in such different parallels, from the 

 tropical and sub-tropical parts of Asia, is eminently singular and 

 peculiar in the character of the plants which inhabit it. The opposite 

 sides of large continents, even where there is continuity of land 

 between the regions, display great diversity of vegetation under 

 almost similar climates, while mountain ranges interposing climatal 

 barriers, cut off closely adjacent countries. Islands lying in the 

 Atlantic exhibit peculiar plants intermixed with others which have 

 come from Africa, Europe, or America, and in proportions agreeing 

 with the contiguity and the identity of climate, modified perhaps by 

 peculiarly constituted diffusing agencies of winds, ocean currents, or 

 birds, in particular cases." 



ON THE ANALOGY BETWEEN THE LIFE OF AN INDIVIDUAL AND 



THE DURATION OF A SPECIES. 



THE following paper was recently read by Prof. Edward Forbes 

 before the Royal Institution, England. 



In natural history and geology, a clear understanding of the rela- 

 tions of individual, species, and genus to geological time and geograpi- 

 cal space is of essential importance. Much, however, of what is 

 generally received concerning these relations will scarcely bear close 

 investigation. Among questionable, though popular notions upon 

 this subject, the lecturer would place the belief that the term of 

 duration of a species is comparable, and of the same kind, w r ith that 

 of the life of an individual. The successive phases in the complete 

 existence of an individual are birth, youth, maturity, decline, and 

 decay, terminating in death. Whether we regard an individual as a 

 single self-existing organism, however produced, or extend it to the 

 series of organisms, combined or independent, all being products of 

 a single ovum, its term of duration can be abbreviated but not pro- 

 longed indefinitely, nor can the several phases of its existence be 

 repeated. Conditions may arrest or hasten maturity, or prematurely 

 destroy, but cannot, however favorable, reproduce a second maturity 

 after decline has commenced. Now, it is believed by many, that a 

 species, (using the term in the sense of an assemblage of individuals, 

 presenting certain constant characters in common, and derived from 

 one original protoplast or stock) passes through a series of phases, 

 comparable with those which succeed each other in definite order 

 during the life of a single individual, that it has its epochs of origin, 

 of maturity, of decline, and of extinction, dependent upon the laws 

 of an inherent vitality. If this notion be true, the theory of geology 

 will be proportionately affected ; since, in this case, the duration of 

 species must be regarded as only influenced, not determined, by the 

 physical conditions among which they arc placed ; and thus species 

 should characterize epochs or sections of time, independent of all 

 physical changes and modifying influences short of those which are 



