tender and delicate, that they did not become opake in distilled vine gar or alcohol, until immersed in these liquors for a considerable time.

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 opake 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.

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 behind; but the form is difficult to assign, as it is varied by partial contractions, at the animal's plea

low, or forms internally an infundibular cavity, which has a wide opening before, and appears also to have a small aperture posteriorIy, through which it discharges its excrements. The posterior two-thirds 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 swim ming, that they appear like the continual passage of a fluid along the ribs. The eiliated 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 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.

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 opake lines, crossed in an

arched

arched manner from the circumference, towards the centre of the animal: an opake irregular shaped process bung 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 tenticula, covered with little 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 Gronovius 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 considered as a distinct species, or as a variety of the hemispherica, I would propose to call it the medusa lucida.

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 of its body are alone luminous.

In the month of September. 1805, I again visited Herne Bay, and frequently 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 beros fulgens. I ob

served 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 phænomenon was extremely dark; many of the medusa scintillans and medusa hemispherica had been observed at low water, 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 little 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.

Captain

Captain Horsburg, in the notes he gave to Sir Joseph Banks, says, there is a peculiar phænomenon 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 phænomenon, he says, is frequently seen in the Banda sea, and is very alarming to those who have never perceived or heard of such an appearance before,

This singular phænomenon 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 Hol-, land to China, about half an hour after sun-set, 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 in soundings, and that the 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 trans-, parent, that they could not be perceived when the hand was taken into the light.

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 phænomenon, 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 important, as it proves that the diffused light of the sea is produced by an assemblage of minute meduse on the surface of the water.

In June 1806, I found the sea at Margate more richly stored with the small luminous medusæ 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 quantity of the luminous water was put into a glass jar, and on standing some time, the medusæ collected at the top of the jar, and formed a gelatinous mass, one inch and a half thick, and of a reddish or

mud

Mayer conjectured that the surface of the sea imbibed 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 Bondaroy believed that it came sometimes from electric fires, but more frequently from the putrefaction of marine animals and plants.

I shall not trespass on the time of the Society to refute the above speculations: their authors have left them unsupported by either arguments or experiments, and they are inconsistent with all ascertained facts upon the 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 speci

mens.

Amongst zoophytes we find, that the genera medusa, beroe, and pennatula, contain species which afford light.

The only animals which appear to possess a distinct organization for the production of light, are the luminous species of lampyris, elater, fulgora, and pausus.

The light of the lampyrides 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 waving outline. I have observed in the glow-worm, that it is absorbed, and its place supplied by a common interstitial substance, after the season for giving light is past.

The segments of the abdomen, behind which this peculiar substance is situated, are thin and transparent, in order to expose the internal illumination.

The number of luminous rings varies in different species of lampyris, and as it would seem at different periods in the same indivi dual.

Besides the luminous substance above described, I have discovered in the common glow-worm, on the inner side of the last abdominal ring, two bodies, which to the naked eye appear more minute than the head of the smallest pin. They are lodged in two slight de

pressions

pressions, 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 ho. mogeneous texture than that which lines the inner surface 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 mem

brane of the respiratory tubes of insects, except that in this case the fibre passes in a spiral instead of a circular direction. This membraue, although so delicately constructed, is so elastic as to preserve its form after the sac is ruptured and the contents discharged.

The light that proceeds from these sacs is less under the control 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.

The circumstance of there being points which give a more permanent light than the other parts of the luminous rings of the abdomen, has been noticed before by the Comte G. de Razoumouski. He states the number of these luminous points to vary from two to five.

I must however remark, that I never saw more than two of these Juminous points, which were al ways upon the last ring of the body, and that the figures which accompany the memoir of the Comte de Razoumouski, bear VOL. LII.

scarcely any resemblance to the insect they are intended to represent; from which we may fairly suspect him of inaccuracy in other. particulars.

As far as my observation has extended, the small sacs of luminous substances are not found in any species of lampyris, except the glow-worm of this country. Thunberg mentions that the lampyris japonica has two vesicles on the tail, which afford light.

The organs for the production of light in the genus elater are situated in the corcelet; these likewise consist of a peculiar yellow substance, placed behind transparent parts of the shell, which suffer the natural colour of this substance to be seen through them in the day, and when illuminated give passage to the light.

On dissecting the organs of light in the elater noctilucus, I found that there is a soft yellow substance, of an oval figure, lodged in the concavity of the yellow spots of the corcelet, which parts are particularly thin and transparent in this specics. This substance is so remarkably close in its structure, that at first view it appears like an inorganic mass, but with a lens it is readily perceived to be composed of a great number of very minute parts or lobules closely pressed together. Around these oval masses, the interstitial substance of the corcelet is arranged in a radiated m nuer, and the fortion of the shell that immediately covers the irradiated substance is in a certain degree transparent, but less so than that which lies over the oval masses: it is therefore probable, that the interstitial substance in this situation may be Tt endowed