Nearly all the other Hydrozoa are marine productions, and comprise among them numerous beautiful forms. Take, for example, the polyp known as _Praya diphyes_, a double, bell‐shaped body, with a long tail, as it were, of feelers, a floating fishing‐line; or, another delicate organisation of the same family, _Galeolaria aurantiaca_, the orange galeolaria. Here are _two_ floating bladders with a connecting _chain of polyps_; the floats aiding to support, as it were, a whole colony! But the large order _Physophoridæ_ deserves more than a mere passing notice, on account of the graceful forms of delicate tissue and colour which are included under it. These inhabitants of the sea are essentially swimmers, having mostly true swimming bladders, more or less numerous and of varied form; they always float on the surface. M. de Quatrefages, the distinguished French naturalist, describing one of these organisms, _Apolemia contorta_, tells the reader “to figure to himself an axis of flexible crystals, sometimes more than a mètre (forty inches) in length, all round which are attached, by means of long peduncles or footstalks equally transparent, some hundreds of bodies, sometimes elongated, sometimes flat, and formed like the bud of a flower. If we add to this garland of pearls of a vivid red colour and infinity of fine filaments, varying in thickness, and giving life and motion to all these parts, we have even now only a very slight and imperfect idea of this marvellous organism.” The _Agalma rubra_ is thus described by Vogt, a great authority. “I know,” says he, “nothing more graceful than this agalma, as it floats near the surface of the waters, its long, transparent, garland‐like lines extended, and their limits distinctly indicated by bundles of a brilliant vermilion red, while the rest of the body is concealed by its very transparency; the entire organism always swims in a slightly oblique position near the surface, but is capable of steering itself in any direction with great rapidity. I have had in my possession some of these garlands more than three feet in length, in which the series of swimming‐bladders measured more than four inches, so that in the great vase in which I kept them the column of swimming‐bladders touched the bottom, while the aërial vesicle floated on the surface. Immediately after its capture the columns contracted themselves to such a point that they were scarcely perceptible, but when left to repose in a spacious vase, all its shrunken appendages deployed themselves round the vase in the most graceful manner imaginable, the column of swimming‐bladders removing, immovable in their vertical position, the float at the surface, while the different appendages soon began to play. The polyps, planted at intervals along the common trunk, of rose‐colour, began to agitate themselves in all directions, taking a thousand odd forms; ... but what most excited my curiosity was the