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communicated to me by others, many of the circumstances attending the luminous appearance of the sea. I shall then describe the organs employed for the production of light in certain species; and, lastly, I shall review the opinions which have been entertained respecting the nature and origin of animal light, and relate the experiments I have made for the purpose of elucidating this part of the subject.
pears probable, that some fishes may have acquired the character of being luminous from evolving light soon after death.
The property of emitting light has been reported to belong to several fishes, more particularly the mackafel, the moon-fish, (tetraodon nola) the dorado, mullet, sprat, &c.
Mr. Bajon observed, during the migration of the dorados, &c. that their bodies was covered with luminous points. These however prov ed, upon examination, to be mere spherical particles that adhered to the surface of these fishes; and, he adds, appeared to be precisely the same sort of points that illuminated the whole of the sea at the time. They were therefore, in all probability, the minute kind of medusa which I shall have occasion to describe hereafter.
Godeheu de Riville states, in a paper sent to the academy of sciences at Paris, that on opening the scomber pelamis while alive, he found in different parts of its body and oil which gave out much light: but it should be observed, that Riville had a particular theory to support, for which this fact was very convenient, and that other parts of his memoir bear marks of inaccuracy. It may be added, that if the oil of fishes were usually luminous, which Riville supposed, it would be almost universally known, instead of resting on a solitary observation.
As far as I am able to determine from what I have seen, the faculty of exhibiting light during life does not belong to the class of fishes. It ap
BELFAST MAG. NO. XXXIIL
I now proceed to the description of those luminous animals that have been discovered by the Right Honourable Sir Joseph Banks, Captain Horsburg, and myself.
On the passage from Madeira to Rio de Janeiro, the sea was observed by Sir Joseph Pauks to be unusually luminous, flashing in many many parts like lightning. He directed some of the water to be hauled up, in which he discovered two kinds of animals that occasioned the phanomenon the one, a crustaceous insect, which he called the cancer fulgens; the other, a large species of medusa, to which he gave the name of pellucens.
The cancer fulgens bears some resemblance to the common shrimp; it is however considerably less; the legs are furnished with numerous sete. The light of this animal, which is very brilliant, appears to issue from every part of the body.
The medusa pellucens measures about six inches across the crown or umbella; this part is marked by a number of opake lines, that pass off from the center to the circumference.
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Journal de Physique, tome XXVIII.
The edge of the umbella is divided into lobules, which succeed each other, one large and two small ones alternately. From within the mar gin of the umbella there are suspended a number of long cord-shap ed tentacula. The central part of the animal is opake, and furnished with four thick irregularly-shaped processes, which hang down in the midst of the tentacula.
This zoophyte is the most splendid of the luminous inhabitants of the ocean. The flashes of light e mitted during its contractions are so vivid as to effect the sight of the spectator.
In the notes communicated to Sir Joseph Banks by Captain Horsburg he remarks that the luminous state of the sea between the Tropics is generally accompanied with the appearance of a great number of marme animals of various kinds upon the surface of the water; to many of which he does not, however, attribute the property of shining. At other times, when the water which gave out light was examined it appeared only to contain small particles of a dusky straw colour, which dissolved with the slightest touch of the finger. He likewise observes that in Bombay, during the hot weather of May and June, he has frequently seen the edges of the sea much illuminated by minute sparkling points.
At sun-rise on April 12, 1798, in the Arabian sea, he perceived several luminous spots in the water, which conceiving to be animals, he went in the boat and caught one. It proved to be an insect somewhat resembling in appearance the wood louse, and was about one third of an inch in length. When viewed with the microscope it seemed to be formed by sections of a thin crustaceous substance. During the time that any fluid remained in the api
In the month of June in the same year he picked up another luminous Insect on a sandy beach, which was also covered with a thin shell, but it was a different shape, and a larger size than the animal taken in the Arabian sea.
By comparing the above description with an elegant pen and ink drawing which was made by Captain Horsburg, and accompanied his paper, I have no doubt that both these insects were monoculi; the first evidently belongs to the genus limulus of Muller; I shall therefore beg leave to distinguish it by the name of limulus noctilucus,
mal it shone brilliantly, like the the water, in consequence of so many fire-fly. points shining at the same moment. When any of these sparkling points were removed from the water, they no longer yielded any light. They were so transparent that in the air they appeared like globules of water. They were more minute than the head of the smallest pin. Upon the slight est touch they broke and vanished from the sight. Having strained a quantity of the luminous water, a great number of these transparent corpuscles were obtained upon the cloth, and the water which had been strained did not afterwards exhibit the least light, I then put some sea-water that had been rendered particularly clear, by repeated filtrations, into a large glass, and having floated in it a fine cloth, on which I had previously collected a number of luminous points, several of them were liberated, and became distinctly visible in their natural element, by placing the glass before a piece of dark coloured paper. They were observed to have a tendency to come to the surface of the water; and after the glass was set by for fome time, they were found congregated together, and when thus collected in a body they had a dusky straw colour, although individually they were so transparent as to be perfectly invisible, except under particular circumstances. Their substance was indeed so extremely tender and delicate, that they did not become opaque in distilled vinegar or alcohol until immersed in these liquors for a considerable time.
My pursuits and the state of my health having frequently led me to the coast, I have had many opportunities of making observations upon the animals which illuminate our own seas. Of these I have discovered three species: one of which is a beroe not hitherto described by authors; another agrees so nearly with the medusa hemispherica that I conceive it to be the same, or at least a variety of that species; the third is a minute species of medusa, which I believe to be the luminous animal so frequently seen by navigators, although it has never been distinctly examined or described.
I first met with these animals in the mouth of October 1804, at Herbe Bay, a small watering place upon the northern coast of Kent. Having observed the sea to be extremely luminous for several nights, I had a considerable quantity of the water taken up. When perfectly at rest, no light was einitted; but on the slightest agitation of the vessel in which the water was contained, a brilliant Scintillation was perceived, particularly towards the surface; and when the vessel was suddenly struck, a flash of light issued from the top of
On examining these minute globules with the microscope, I found that they were not quite perfect spheres, but had an irregular depression on one side, which was formed of an opaque substance, that projected a little way inwards, producing such an appearance as would arise from tying the neck of a round
bag, and turning it into the body.
The motions of these creatures in the water were slow and graceful, and not accompanied by any visible contraction of their bodies. After death they always subsided to the bottom of the vessel.
gently near the surface of the water, its whole body became occasionally illuminated in a slight degree; during its contractions a stronger light issued from the ribs; and when a sudden shock was communicated to the water, in which several of these animals were placed, a vivid flash was thrown out. If the body were broken, the fragments continued luminous for some seconds, and being rubbed on the hand, left a light like that of phosphorus: this however, as well as every other mode of emitting light, ceased after the death of the animal.
From the sparkling light afforded by this species, I shall distinguish it by the name of medusa scintillans.
The night following that on which I discovered the preceding animal, I caught the two other luminous species. One of these I shall call the beroe fulgens.
This most elegant creature is of a colour changing between purple, violet, and pale blue; the body is truncated before, and pointed be hind; but the form is difficult to assign, as it is varied by partial contractions, at the animal's pleasure, I have represented the two extremes of form that I have seen this creature assume: the first is somewhat that of a cucumber, which, as being the one it takes when at rest, should perhaps be considered as its proper shape: the other resembles a pear, and is the figure it has in the most contracted state. The body is hollow, or forms internally an infundibular cavity, which has a wide opening before, and appears also to have a small aperture posteriorly, through which it discharges its excrement. The posterior twothirds of the body are ornamented with eight longitudinal ciliated ribs, the processes of which are kept in such a rapid rotatory motion, while the animal is swimming, that they appear like the continual passage of a fluid along the ribs. The ciliated ribs have been described by Professor Mitchell, as arteries, in a luminous beroe, which I suspect was no other than the species I am now giving an account of. When the beroe fulgens swam
The hemispherical species that I discovered, had a very faint purple colour. The largest that I found measured about three quarters of an inch in diameter. The margin of the umbella was undivided, and surrounded internally by a row of pale brown spots, and numerous small twisted tentacula; four opaque lines crossed in an arched manner from the circumference, towards the centre of the animal: an opaque irregular-shaped process hung down from the middle of the umbella; when this part was examined with a lens of high powers, I discovered that it was inclosed in a sheath in which it moved, and that the extremity of the process was divided into four tentacula, covered with litthe cups or suckers, like those on the tentacula of the cuttle-fish.
This species of medusa bears a striking resemblance to the figures of the medusa hemispherica, published by Gonovius and Muller; indeed it differs as little from these figures, as they do from each other. Its luminous property, however, was not observed by these naturalists, which is the more extraordinary; as Muller examined it at night, and says it is so transparent, that it can only be seen with the light of a lamp. If it should be still consi
In this species, the central part and the spot round the margin, are commonly seen to shine on lifting the animal out of the water into the air, presenting the appearance of an illuminated wheel, and when it is exposed to the usual percussion of the water, the transparent parts cha of its body are alone luminous.
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distance from me: he also perceived it, and called out to me at the same instant. On both these occasions the flash was visible for about four or five seconds, and although I watched for it a considerable time, I did not see it repeated.
A diffused luminous appearance of the sea, in some respects different from what I have seen, has been described by several navigators.
Godeheu de Riville saw the sea assume the appearance of a plain of snow on the coast of Malabar.
dered as a distinct species, or as a variety of the hemispherica, I would propose to call it the medusa lucida.
In the month of September, 1805, again visited Herne Bay, and fre quently had opportunities of witnessing the luminous appearance of the sea. I caught many of the hemispherical and minute species of medusa, but not one of the beroe fulgens. I observed that these luminous animals always retreated from the surface of the water, as soon as the moon rose. I found also, that exposure to the day-light took away their property of shining. which was revived by placing them for some time in a dark situation.
In that season I had two opportunities of seeing an extended illumination of the sea, produced by the above animals. The first night I saw this singular phenomenon was extremely dark; many of the medusa scintillans and medusa hemispherica had been observed at lowwater, but on the return of the tide, they had suddenly, disappeared. On looking towards the sea, I was astonished to perceive a flash of light of about six yards broad, extend from the shore, for apparently the distance of a mile and a half along the surface of the water. The second time that I saw this sort of light proceed from the sea, it did not take the same form, but was diffused over the surface of the waves next the shore, and was so strong, that I could for the moment distinctly see my servant, who stood at a Kittle
Captain Horsburgh, in the notes he gave to Sir Joseph Banks, says, there is a peculiar phenomenon sometimes seen within a few degrees distance of the coast of Malabar, during the rainy monsoon, which he had an opportunity of observing. At midnight the weather was cloudy, and the sea was particularly dark, when suddenly it changed to a white flaming colour all around. This bore no resemblance to the sparkling or glowing appearance he had observed on other occasions in seas near the equator, but was a regular white colour, like milk, and did not continue more than ten minutes. A similar phenomenon, he says, is fre quently seen in the Banda sea, and is very alarming to those who have never perceived or heard of such an appearance before.
This singular phenomenon appears to be explained by some observations communicated to me by Mr. Langstaff, a surgeon in the city, who formerly made several voyages. In going from New Holland to China, about half an hour after sunset, every person on board was astonished by a milky appearance of the sea: the ship seemed to be surrounded by ice covered with snow. Some of the company supposed they were
• Mem. Etrang. de l'Acad. des Stay Tom. 3.