Both these corals seem to have been _fissiparous_, that is to say, they propagated by splitting into two parts, each of which formed the base of a new column with a new animal. The evidence for this statement rests on the fact, that many of the tubes are seen to bifurcate in their course, so that two new tubes are produced equal in size and completeness to the old one from which they proceed. Another mode of generation which, in at least its earlier stages, would produce a somewhat similar appearance is called _gemmation_, and consists in the protrusion of a bud or gemmule from the side of the animal, which shortly develops into a new and perfect individual. It is probable, however, that the ordinary mode of propagation among these old corals was the usual one by impregnated ova. These ova, like those of our sea-anemones, were probably generated within the partitions, between the central stomach and the outer wall, whence they passed down into the stomach, and were ejected by the mouth of the parent as little gemmules, furnished with the power of locomotion by means of vibratile cilia. Some of the _Medusa_ family possess this three-fold mode of propagation; but, in all, the last-mentioned is the most usual. Has the reader ever stretched himself along the shore, while, perhaps, a July sun blazed overhead, and a fitful breeze came over the sea, just strong enough to chase ashore an endless series of rippling wavelets, and breathe over his temples a delicious and refreshing coolness? Thus placed, and gazing dreamily now, perchance, at the distant sails like white specks along the boundary line of sea and sky; now at the gulls wheeling in broad circles through the air, and shooting swift as arrows down into the blue water, he must often have turned to look for a little at the sand which, heaped up in little mounds around him, formed a couch well-nigh as soft as the finest down. Many a varied fragment entered into the composition of that sand. Mingled among the minuter quartzy particles lay scores of shells, some with the colour not yet faded, and the valves still together--the delicate tellina, with its polished surface, and its flush of pink; the cardium with its strong white plaited sides, and the turritella with its circling spire; some were worn down and sorely effaced, others broken into fragments by the ceaseless grinding of the waves. It was pleasant labour in such a sultry noon to pick out the shells of one species in all stages of decay. The _Trochus lineatus_, or Silver Willie, as young ramblers by the sea-shore love to call it, showed well the process of destruction. The perfect shell, cast ashore, perhaps, by the last storm, and still uninjured by the tides, displayed its russet epidermis, or outer skin, covered with fine brown zig-zag lines, running across the whorls from the creature's wide pearl-lined mouth to the apex. A second shell exhibited a surface that had begun to suffer; the point had been