or floated by currents. The remarkable limitation of certain species to single spots on the globe seems to favor the supposition of specific centres.” [35] _Rhodomenia palmata_ and _Alaria esculenta_. [36] _Porphyra laciniata_, _Chorda filum_, and _Enteromorpha compressa_. [37] “Dr. Neill mentions,” says the Rev. Mr. Landsborough, in his complete and very interesting “History of British Sea-Weeds,” “that on our shores algæ generally occupy zones in the following order, beginning from deep water:—_F. Filum_; _F. esculentus_ and _bulbosus_, _F. digitatus_, _saccharinus_, and _loreus_; _F. serratus_ and _crispus_; _F. nodosus_ and _vesiculosus_; _F. canaliculatus_; and, last of all, _F. pygmæus_; which is satisfied if it be within reach of the spray.” [38] We are supplied with a curious example of that ever-returning cycle of speculation in which the human mind operates, by not only the introduction of the _principle_ of Epicurus into the “Vestiges,” but also by the unconscious employment of even his very _arguments_, slightly modified by the floating semi-scientific notions of the time. The following passages, taken, the one from the modern work, the other from Fénélon’s life of the old Greek philosopher, are not unworthy of being studied, as curiously illustrative of the cycle of thought. Epicurus, I must, however, first remind the reader, in the words of his biographer, “supposed that men, and all other animals, were originally produced by the ground. According to him, the primitive earth was fat and nitrous; and the sun, gradually warming it, soon covered it with herbage and shrubs: there also began to arise on the surface of the ground a great number of small tumors like mushrooms, which having in a certain time come to maturity, the skin burst, and there came forth little animals, which, gradually retiring from the place where they were produced, began to respire.” And there can be little doubt, that had the microscope been a discovery of early Greece, the passage here would have told us, not of mushroom-like tumors, but of monads. Save that the element of microscopic fact is awanting in the one and present in the other, the following are strictly parallel lines of argument:—