ORGAN-PIPE.

Every one of these stories has been formed in succession. From the tips of some of the tubes we see protruding an elegant polype of an emerald-green hue, having eight starry tentacles, and giving off from its base an enveloping membrane, which spreads over the rim of the tube and descends on the outside to the floor. By means of this vascular membrane, both tube and floor have been formed. Calcareous particles, deposited, one by one, in its substance, gradually built up the tube of the primary polype, or probably the tubes of the first series, the basement or ground-floor. When these tubes had arrived at a certain height, all simultaneously began to develope the fleshy membrane horizontally, which expanded until that from each touched that from its neighbour, with which it united. Meanwhile the calcareous deposition went on in this horizontal layer, and thus the first floor was made.

Now from the living vascular upper surface of this layer sprang up at certain spots buds,[62] offshoots of the common flesh, which soon rose into columns, and, by a process of calcareous deposition, became tubes with terminal polypes, which in turn spread out a horizontal layer, and thus the second floor was built. Hence a new race of polypes budded, which by and by formed the third floor; and so on in succession, until the series had attained the height which we see.

If we assume one of these stories to be the growth of a year,[63] we have ocular evidence in this specimen of six years' age, for here are six successive floors. But no: for it was created complete, as we see it, this very hour.

Yonder goes a Medusa, pumping its way laboriously, yet not ineffectively, just beneath the surface of the clear wave. It is a great affair, nearly a foot in diameter. Have we, from merely examining its appearance and structure, any criterion by which we can guess whether it has lived an hour, or a year, or ten years? Surely we have; for this mass of clear jelly is composed, like all other organic bodies, of cells, which have been gradually generated, by nutrition and assimilation, from the embryo.[64] This process must have occupied many months, if not several years; but the history of this Medusa did not begin when it took its present umbrella-like form. Shall we trace it back a little farther?

At some time back, then, this creature detached itself as the terminal one of many little saucer-like bodies, which had been for some time previously forming by the gradual constriction of a thick fleshy stem. Before the constriction began to be visible, this stem was the body of a white Hydraform polype, affixed by its base, and furnished at its free extremity with thirty-two tentacles. It had lived several years in this form, developing many Hydroid polypes, just like itself, by successive gemmations. Before it took this shape, which it assumed gradually, its tentacles being developed in geometrical progression, 32 from 16, from 8, from 4,—it was a soft ovoid planule clothed with vibratile cilia, which swam freely in the sea, like an Infusorium.

Thus the physiologist would confidently assign to this Medusa an existence of several years, as an independent organism; nor could his conclusions be controverted, except by the knowledge of the fact that the Medusa has been but just now created.

We pass on. Here is an Echinus. Let it be borne in mind still, that we have, in idea, the power of pursuing our researches on each creature at the moment which follows that of its creation; and that, when that actually was is of no consequence to our investigation.