A Year at the Shore

by Philip Henry Gosse

The following appearances proved the luminosity of this beautiful Æquorea, on being subjected to experiments in the dark. When with my finger-nail I tapped the glass jar in which two specimens were floating at the surface, instantly each became brilliantly visible as a narrow ring of light, the whole marginal canal becoming luminous. On my touching them with the end of a stick, the light became more vivid, and round spots appeared here and there in the ring, of intense lustre and of a greenish-blue tint. These were, I doubt not, the tentacle-bulbs; and any one of them would be excited to this intensity by my touching that part of the margin with the stick. The luminosity of the ring was not so evanescent as in some species, lasting several seconds, and continuing to be renewed as often as I molested the animal. The two circles of light, two inches or more in diameter, were very beautiful as they moved freely in the water, sinking or rising according as they were touched, now seen in full rotundity, now shrinking to an oval, or to a line, as either turned sidewise to the eye, and reminded me of the coronæ of glory in the pictures of the Italian school, round the heads of saints.

CRIMSON-RINGED JELLY-FISH.

Most of the larger Medusæ of our coasts belong to another order, including those which have covered eyes, and some other peculiarities, chiefly connected with reproduction. The Lucernariæ, which I have already noticed, formerly associated with the Anemones, are now united with this order. A very familiar example we may see in our harbours and tidal rivers in summer, the common Crimson-ringed Jelly-fish.[130] It is a hemisphere of colourless jelly, some six or eight inches in diameter, which is usually well marked by four imperfect rings of purplish crimson—the reproductive organs—seen through the transparent flesh. The radiating vessels are often tinged with the same colour.

Plate 30.
P. H. GOSSE, del. LEIGHTON, BROS.
CYDIPPE. COMMON MEDUSA. LARVAL FORMS.

INFANT FORMS.

The most interesting circumstances in the history of this large jelly-fish are the wonderfully varied phases through which it passes in the earlier stages of its existence. Along the margins of the lengthened flaps of the polypite there are found remarkable pouches, within which the ova are placed, and whence they are hatched in the form of soft flat animalcules, capable of swimming by means of cilia. This has been called a planula. After swimming a while, it alters its form to that of a pear, and presently adheres by its slender end to a sea-weed or rock under water, hanging downward. A depression now appears in the larger end, which deepens and forms a mouth and stomach, and the little planula has assumed a polype-form. Four tiny warts now spring from the margin of the mouth, which lengthen into tentacles; four more then shoot in the interspaces; these eight increase to sixteen, then to thirty-two, all at the same time acquiring great length. In this stage, in which it is very common in our aquaria, it has been supposed a new animal, and has been named Hydra tuba. The space between the margin and the mouth has widened into an “umbrella,” and the mouth has protruded into a polypite. The whole is of a translucent white hue, and the body without the tentacles is ordinarily about one-sixth of an inch high.

This stage sometimes lasts for years without further change, except that creeping root-threads shoot from the attached base, which send up at intervals buds that grow into Hydræ; and buds break out from different parts of the body itself, which likewise develop themselves, the form in both cases being exactly similar to that of the present Hydra tuba. Thus we frequently find numerous colonies of these tiny creatures crowded together.

At length a change takes place. The body enlarges both in length and thickness, and begins to show traces of rings or segments, as if it had been tied tightly round with threads at regular intervals. In this stage it has been described under the name of Scyphistoma. These cuts deepen, and the segments thus marked off become hollow; and so they resemble a pile of tiny saucers set one within another, each of which is now divided at its rim into eight teeth. In this stage it has been once more named, as if an independent animal, Strobila.