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Otago Witness, Issue 1851, 17 August 1893, Page 49

The Marvel of Living

By Dinornis.

A great many carious things are now known about the development of invertebrate or backbonelesa animals, which formerly it was not possible could be known. I refer more particularly to marine animals, as very little was known about the strange changes that many of them undergo until quite recently. There were many fancies and fables, but very little of anything else until naturalists took to the ocean as afield of research on the one hand, and to the keeping of scientific aquaria on the other.

When we come to observe the development of the common jelly-fish or medusa, we learn some things whichbear upon tbe whole of liviDg nature beside. Tbe jelly-fish is the wateriest of all animals, the proportion of solid matter in its body being as 1 in 400. It is composed of a few films of solid matter, and all the rest water. Some of the large ones are very bulky. 3peoimens I have picked up, stranded on the beacb, must have weighed about 201b, but if such a one was laid out on a board exposed to the sun, in a short time only a thin papery sheet of fragile tissue would, be left, and this could be put between the leaves of a book much as we put the leaves or petals of flowers. Everyone has heard the story of the ignorant farmer who discovered a great number of jelly-fishes lying on the beach one day. He thought they would make first-rate manure for his fields, so hastily carted a lot of them to the farmyard. But in a day or two what was at first a great mass had entirely disappeared, a result which the poor man was fain to attribute to hobgoblin agency. It is said to be a fact thatafter a jelly-fish weighing 21b hashad tbe water strained out of it the 'solid matter weighs about 30gr. Yet in its life history as strange and curious changes tako plaoe as

happens to any other creature that lives. Indeed, in regard to certain aspects of its development it may be said that they have a special interest of their own, supplying as they do a kind of starting point from which to trace the evolution of some of the more special organs characteristic of the higher animals. In the case of the amoeba and such lower forms it is quite obvious that they possess no organs at all. Neither design nor contrivance is suggested by the contemplation of such organisms, but they have substance and life. The substance we can analyse and resolve into variousi chemical constituents, but it is otherwise with life. The living substance, protoplasm, of which the amoeba is composed has "within itself all powers necessary to the highest animals. The difference is that it has not applied the division of labour principle in its economy, while the higher animals have done so, and become higher animals in the doing of it. However, to come back to our jelly-fish. Like a great many other marine animals, it begins separate existence as a small swimming egg ovplanula, and after a while this changes to a trumpet-like form with a depression in the centre of the thick end. It is very small— only about in height during this stage— and it is nothing like a jelly-fish. When it has undergone full development it may become an enormous animal 7ft across, and with tentacles 50ft long, but it is a long way from that yet. After sporting around for a while — seeing the world, so to speak — it seems to grow somewhat sick of it all. It sits down on a ropk or other suitable position on the sea- floor and appears to take root there. It loses the power of free motion, and in a short time it gets to look quite a different being. It sits on its thinnest end, and the hollow part at the top grows deeper. Eound its rim also little knobs begin to show themselves, and by-and-bye these become tentacles containing thread-cells as in hydra. As time rolls on— and the animal may remain in this stage for several years — these tentacles are augmented by another set, which grow in the spaces between the firstformed ones. It increases in length, and becomes very like a hydra indeed. Of course it developes a mouth— a very capacious one for its size— and uses its tentacles just as the hydra does to draw in food. Like Longfellow's village blacksmith, it "earns whate'er it can"; when it can get nothing to eat it does very well without food for a

while, only that means delay in its progress towards its goal. Having grown sufficiently, its body becomes marked by corrugations as shown in the diagram, and it assumes what has been called the " pile of saucers " stage. It is a pretty object now, as well as a most extraordinary one. The original set of tentacles fall off as the " saucers " attain full growth, and a new set grows near the base. Soon the topmost segment, or "saucer," loosens iteelf, turns over, and floats away, and all the others in their turn imitate its example. While still young, if these small forms be dredged up with a fine

net, the most able naturalist conld not tell whether he had before him young jellyfishes or the larval forms of certain other sea animals. Each one, if it meet with no accident of a kind to cut short its career, grows rapidly until the enormous dimensions .formerly alluded to are attained. Tbe knobby projections on the saucer-edge become tentacles, and other parts are correspondingly developed. Stranded on a seabeach it may look a mere gelatinous squab, but seen swimming in the clear water it is really a most beautiful object. Every part is distended, smooth, symmetrical ; it moves along gracefully, though slowly, with a rhythmic motion, contracting and expanding its rudimentary muscles in response to the stimulus of primitivenerves — oftbesamekind, if not of the same quality, as those which control the muscles of our own bodies. Bound the rim of its swimming .bell are also to be observed spots of colour, which there is no reason now to doubt are primitive-eyes. Closer scrutiny discloses another row of spherical organs called " litho-cys'ts," or stone cells, which are really about the most primitive hearing organs known.

The medusa, having now reached its perfect state, and having a good big mouth and a comprehensive digestive system, swims about in search of prey, and its lotig tentacles being full of thread-cells it is well equipped to find it. The thread-cells of medusa are of a more complex and efficient sort than those of hydra; they are double, as in addition to the spiral spring there is also in each a " poison dart," and when the tentacle is irritated the double artillery is discharged at the same moment. Ido not know that the medusa preys upon any but small, soft fry, but I do know that to have a score or two of these darts let fly at one's ficgers gives a lively idea of tbe jelly-fish's way of overcoming its victims, and also of bow it comes to be known by the name of " sea nettle." Having eaten a large quantity oC provisions and grown enormously bulky, like the butterflies it develops a lot of eggs, and when they are freed it dies. Each egg becomes a planula, and the whole process is repeated. Now, what do these changes mean ? Why does not like in this instance produce like ? Why should the free swimming medusa

spend so many of its early days as a vege-table-like organism fixed to a rook 7 And! why, in its stages of growth and development, does it sometimes appear so like certain other animals— the hydra, for instance—somewhat lower than itself in the scale of life? And why, when it first floats a way from off the " pile of saucers," should it be entirely indistinguishable from the larval forms of other animals— the "sea fir" particularly, which in its adult state isa plant-like compound organism living upon seaweed or stones ? Men who have devotei a great deal of attention to the study of medusa tell us that in tracing the course of these developments we will assuredly find good reason for the belief that these animal families are not divided by any sharplydrawn line, but that they are related to eachother, and that somewhere in their ancestral history they had a common origin. Their relationship may be by no means obvious while we compare the adult forms only, but it is forced upon us as we watch tbe earlier stages of evolution of these various species. It may be said with truth that I bave hardly approached the subject of this paper. It is unapproachable, unsolvable. We can only know about living things, not about life. Famous naturalists have given years to tho study of the jelly-fish, and still there is a great deal to learn. When all is known about it that is to be known the mystery and marvel of life will be as great as ever. It will be even greater, for the more that is known the greater does this marvel ever become.