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in soundings, and that coral bottom gave this curious reflection; but on sounding with 70 fathoms of line, no bottom was met with. A bucket of water being hauled up. Mr. Langstaff examined it in the dark, and discovered a great number of globular bodies, each about the size of a pin's head, linked together. The chains thus formed did not exceed three inches in length, and emitted a pale phosphoric light. By introducing his hand into the water, Mr. Langstaff raised upon it several chains of the luminous globules, which were separated by opening the fingers, but readily re-united on being brought again into contact, like globules of quicksilver. The globules, he says, were so transparent, that they could not be perceived when the hand was taken into the light.
into a glass jar, and on standing some time, the medusa collected at the top of the jar, and formed a gelatinous mass, one inch and a half thick, and of a reddish or mud colour, leaving the water underneath perfectly clear.
In order to ascertain if these animals would materially alter their size, or assume the figure of any other known species of medusa, I kept them alive for 25 days, by carefully changing the water in which they were placed; during which time, although they appeared as vigorous as when first taken, their form was not in the slightest degree altered, and their size but little increased. By this experi ment I was confirmed in the opinion of their being a distinct species, as the young actinia and medusæ exbibit the form of the parent in a much shorter period than the above.
In September, 1806, I took at Sandgate a number of the beroe fulgens, but no other species: they were of various dimensions, from the full size down to that of the me dusa scintillans: they could however be clearly distinguished from the latter species, by their figure.
Since that time, I have frequently met with the medusa scintillans on different parts of the coast of Sussex, at Tenby, and at Milford haven. I have likewise seen this species in the bays of Dublin and Carlingford, in Ireland.
In the month of April, last year, I caught a number of the bero fulgens in the sea at Hastings; they were of various sizes, from about the balf of an inch in length to the bulk of the head of a large pin. I found many of them adhering together in the sea; some of the larger sort were covered with small ones, which fell off when the animals were handled, and by a person unaccustomed to observe these creatures, would
This extraordinary appearance of the sea was visible for two nights. As soon as the moon exerted her influence, the sea changed to its natural dark colour, and exhibited distinct glittering points, as at other times. The phenomenon, he says, had never been witnessed before by any of the company on board, although some of the crew had been two or three times round the globe.
I consider this account of Mr. Langstaff very interesting and im portant, as it proves that the diffused light of the sea is produced by an assemblage of minute medusa on the surface of the water.
In June, 1806, I found the sea at Margate more richly stored with the small luminous medusa, than I have ever seen it. A bucket of the water being set by for some time, the animals sought the surface, and kept up a continual sparkling, which must have been occasioned by the motions of individuals, as the water was perfectly at rest. A small quanity of the luminous water was put
have been taken for a phosphoric substance. On putting a number of them into a glass, containing clear sea water, they still shewed a disposition to congregate upon the surface. I observed that when they adhered together, they shewed no contractile motion in any part of their body, which explains the cause of the pale or white colour of the diffused light of the ocean. The flashes of light which I saw come from the sea at Herne bay, were probably produced by a sudden and general effort of the medusa to separate from each other, and descend in the water.
and had no knowledge of the other. Some navigators have actually described this species of medusa, without being aware of its nature. Mr. Bajon, during his voyage from France to Cayenne, collected many luminous points in the sea, which, he says, when examined by a lens, were found to be minute spheres. They disappeared in the air. Doctor Le Roy, in sailing from Naples to France, observed the sparkling appearance of the sea, which is usu ally produced by the medusa scintillans. By filtering the water, he separated luminous particles from it, which he preserved in spirits of wine: they were, he says, like the head of a pin, and did not at all resemble the nereis noctiluca, described by Vianelli; their colour approached a yellow-brown, and their substance was extremely tender, and fragile. Notwithstanding this striking resemblance to the medusa scintillans, Le Roy, in consequence of a preconceived theory, did not suppose what he saw were animals, but particles of an oily or bituminous nature*.
The medusa scintillans almost constantly exists in the different branches of Milford haven that are called pills. I have sometimes found these animals collected in such vast numbers in those situations, that they bore a considerable proportion to the volume of the water in which they were contained: thus, from a gallon of sea-water in a luminous state, I have strained above a pint of these medusæ. I have found the sea under such circumstances to yield me more support in swimming, and the water to taste more disagreeably than usual; probably the difference of density, that has been remarked at different times in the water of the sea, may be referred to this
All my own observations lead me to conclude, that the medusa scintillans, is the most frequent source of the light of the sea around this country, and by comparing the accounts of others with each other, and with what I have myself seen, I am persuaded that it is so likewise in other parts of the world. Many observers appear to have mistaken this species for the nereis noctiluca, which was very natural, as they were prepossessed with the idea of the frequent existence of the one,
The minute globules seen by Mr. Langstaff in the Indian ocean, were, I think, in all probability, the sciutillating species of medusa; and on my shewing him some of these animals I have preserved in spirits, he entertained the same opinion.
Professor Mitchell, of New York, found the luminous appearance on the coast of America, to be occa sioned by minute animals, that from his description, plainly belonged to this species of medus, notwithstanding which, he supposed them to be a number of the nereis noctilucat.
The luminous animacile discover
• Observ. sur un lumiere produite par L'Eau de la mer. Mem. Etrang. des Sc. ↑ Phil. Mag. Vol. X. p. 20.
putrefaction of marine animals and plants.
I shall not trespass on the time of the Society to refute the above speculations; their authors have lek them unsupported by either argó ments or experiments, and they are inconsistent with all ascertained facts upon this subject.
The remarkable property of emitting light during life, is only met with amongst animals of the four last classes of modern naturalists, viz. Mollusca, Insects, Worms, and Zoophytes.
The mollusca and worms contain each but a single luminous species the pholas dactylus in the one, and the nereis noctiluca in the other.
Some species yield light, in the eight following genera of insects: clater, lampyris, fulgora, pausus, scolopendra, cancer, lynceus*, and limulus. The luminous species of the genera lampyris and fulgora are more numerous than is generally supposed, if we may judge from the appearance of luminous organs, to be seen in dried specimens.
Amongst zoophytes we find that the genera medusa, beroet, and pennatula, contain species which afford light.
ed by Forster off the Cape of Good Hope, in his Voyage round, the World, bears so strong a resemblance to the medusa scintillans, that I am much disposed to believe then the same. He describes his animalcule as being a little gelatinous globule, less than the head of a pin; transparent, but a little brownish in its colour; and of so soft a texture that it was destroyed by the slightest touch, On being highly magnified, he perceived on one side a depression, in which there was a tube that passed into the body, and commuuicated with four or five intestinal sacs. The pencil drawings he made on the spot, are in the possession of Sir Joseph Banks, by whose permission, engravings from them are subjoined to this paper. By comparing these with the representations of the medusa scintillans, and some of this species rendered visible, by being a long time preserv ed in spirits, which I have laid before this learned society, it will be found, that the only difference between Forster's animalcule, and the medusa scintillans, is in the ap pearance of the opaque parts, shewn in the microscopic views.
Many writers have ascribed the light of the sea to other causes than luminous animals. Martin supposed it to be occasioned by putrefaction; Silberschlag believed it to be phosphoric; Professor J. Mayer conjectured that the surface of the sea imbided light, which it afterwards discharged. Bajon and Gentil thought the light of the sea was electric, because it was excited by friction. Forster conceived that it was sometimes electric, sometimes caused from putrefaction, and at others by the presence of living animals. Fougeroux de Eondaroy believed that it came sometimes from electric fires, but more frequently from the
The only animals which appear to possess a distinct organization for the production of light, are the h minous species of lampyris, elater, fulgora, and pausus.
The light of the lampy rides is known to proceed from some of the last rings of the abdomen, which, when not illuminated, are of a pale
yellow colour. Upon the internal surface of these rings there is spread a layer of a peculiar soft yellow substance, which has been compared to paste, but by examination with a lens I found it to be organized like the common interstitial substance of the insect's body, except that it is of a closer texture, and a paler yellow colour, This substance does not entirely cover the inner surface of the rings, being more or less deficient along their edges, where it presents an irregular wav. ing ontline. I have observed in the glow-worm that it is absorbed, and its place supplied by common interstitial substance, after the season for giving light is past.
The segments of the abdomen, be hind which this peculiar substance is situated, are thin and transparent, in order to expose the internal illumination.
pear more minute than the head of the smallest pin. They are lodg ed in two slight depressions, formed in the shell of the ring, which is at these points particularly transparent. On examining these bodies under the microscope I found that they were sacs containing a soft yellow substance, of a more close and homogeneous texture than that which lines the inner subface of the rings. The membrane forming the sacs appeared to be of two layers, each of which is composed by a transparent silvery fibre, in the same manner as the internal membrane of the respiratory tubes of insects; except that in this case the fibre passes in a spiral instead of a circular direction. This membrane, although so delicately constructed, is so elastic as to preserve its form af ter the sac is ruptured and the contents discharged.
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The light that proceeds from these sacs is less under the controul of the insect than that of the luminous substance spread on the rings: it is rarely ever entirely extinguished in the season that the glow-worm gives light, even during the day; and when all the other rings are dark, these sacs often shine brightly.
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