A Paper on “Medusæ” – the fifth in a series on the Lower Forms of Animal Life – was read by Mr. J. M. Kirk.

Medusæ, or Jelly fish, have many of the characteristics of the common fresh-water Hydra, so easily obtainable. The green Hydra is composed of a small tubular sac, closed at one end, open at the other, and having round this opening from six to ten tentacles, vert slender. The tubular sac is the body of the animal, the opening is at once the mouth and the entrance to the digestive canal.

The hydra appear to have no lungs, liver, intestines, nervous system nor heart. They have no organ of the senses, except those which may exist in their mouth and skin. The arms are hollow and communicate with the stomach. They are provided with vibratile cilia and are furnished with a large number of stinging thread-like cells, which when the animal is irritated, are thrown out.

The green hydra has thus a very simple organisation. Their multiplication takes place in three different ways – by eggs, by buds after the manner of vegetables, and by separation, in which an individual may be cut in two or more pieces, each reproducing a perfect animal.

On the seashore at low-tide, may often be seen ugly jelly-like lumps of a greenish colour. These are Medusæ.

When seen suspended in the middle of the waves, like a bell of gauze, terminating in delicate, silvery garlands, we must be struck with their beauty.

They are found in the seas of every latitude, and are, of all animals, those which present the least solid substance. Their bodies are little else than water which is scarcely retained by an imperceptible organic net-work. Their bodies are transparent jelly almost without consistence. Yet in the Artic seas they are one of the principal supports of the whale. Their innumerable masses sometimes cover several square leagues in extent. Many species are Phosphorescent during the night. Most of them produce an acute pain when they touch the human body.

The method of reproduction in the Rose Aurelia, a beautiful variety of a pale rose colour, is as follows. It lays eggs, which are transposed into oval larvæ, They swim about for a short time, with great rapidity, much like some of the infusoria, which they strikingly resemble in other respects. In forty-eight hours these movements decrease, and the larval form attaches itself to some solid body, gumming itself to it. A change of form soon takes place: it becomes elongated; its stalk is contracted, and the other end swells into a sort of cup. An opening soon appears, through which an internal cavity is seen. Four little protuberances have now appeared on the edge, which are, in time, lengthened into arms. Others soon follow; these are the tentacles of a polyp which the young infusorian has now become. The young Medusa lives sometime under this form. It next becomes cylindrical and divided into ten to fourteen rings, which are at first smooth, but soon become pointed at the edges. The animal resembles a pile of plates cut round the edges. In a short time, each ring is slightly raised at the fringed edge, which becomes contractile. Finally the disc becomes detached and begins to swim. They assume their umbrella shape, digestive organs develop, a mouth opens, the tentacles enlarge, the fringe grows, and after all these metamorphoses, the Medusa appears, perfectly resembling, not the parent form, but that form from which its parent originally sprung.

A few years ago, a small Medusa, varying from a line to half-an-inch in diameter was found in the Tropical fresh-water lily tank at the London Royal Botanic Society’s Gardens. The water is kept at 86 deg. Fahrenheit. This was probably the Medusoid form of a hydroid Zoophyte, part of the development of these plant animals including a form similar to that of the Medusa or Jelly-fish. It is probably the only instance of a Medusa which can live in perfectly fresh water, and which dies in cold or salt water.

The Medusae proper are each separate and complete animals, but there are many free-swimming oceanic forms, in which the apparent individual is really a colony.

The paper was illustrated by a large number of drawings – specially prepared by the author.