Many years ago Dr. Milne‐Edwards, in a voyage round the coast of Sicily, employed a diver’s apparatus to enable him to descend and examine the bottom of the sea. It included a metallic casque and helmet, with visor or window of glass fitting closely by means of water‐tight packing round the neck. It communicated with an air‐pump above by a flexible tube; the diver had a rope attached by which he could be hoisted immediately, and a signal cord to give alarm in case of need; he wore heavy lead shoes, which gave him steadiness and enabled him to maintain his upright position in the water. Milne‐Edwards made the descent in several fathoms of water, and with perfect safety. Ariel’s song had not to be applied to him:— “Full fathoms five thy father lies; Of his bones are coral made; Those are pearls that were his eyes. Nothing of him that doth fade But doth suffer a sea change”— for he was enabled safely and successfully to examine in the most hidden recesses and retreats of the rocks and sea many wonderful creatures, the knowledge of which had been hitherto hidden from the scientific world. The invention, or introduction rather, of the salt‐water aquarium enables any one nowadays to study in comfort and at leisure the habits and peculiarities of marine animals. There is a drawing extant of an aquarium bearing the date 1742. Sir John Graham Dalyell, a well‐known author, had a modest one early in this century. A sea‐anemone taken from the sea in 1828, and placed in this glass tank, was, according to his biographer, alive and well in 1873; so that M. Figuier in claiming its first suggestion for M. Charles des Moulins is wrong. The fact is that the ancients kept, not for scientific, but for gastronomic purposes, fish and molluscs in tanks, and fed and studied their habits and needs in order to fit them for the table. These were practical aquaria. M. des Moulins, however, and, in our own country, Gosse and Warington, deserve full credit for advocating the establishment of these beautiful sources of rational pleasure and improvement, and for showing how they might best be kept in working order. To Des Moulins is also due the proposition that the animal life therein required the presence of vegetable life to keep it in natural condition. In the fresh‐water aquarium duckweed was found to act efficiently, and a similar idea is now adopted in regard to marine plants in the salt‐water aquarium. Sea‐weeds do not usually bear transplanting, but sea water is so impregnated with seeds or germs, that by placing a few stones or rocks in the tank a crop of marine vegetation is ensured. “On shell or stone is dropped the embryo seed, And quickly vegetates a vital breed.”