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furnished with a vesicle at their base. Suckers are found word. In Rhizostoma, for instance, the only communicaat the extremities and along the sides of these tentacles in tion between the stomach and the outer surface is carried several of the genera, so as to enable them more securely to on through numerous branching canals in the pensile arms. catch the floating destined prey, or to assist in anchoring The orifices by which these open externally are very minute; the Medusa when it would rest, as we have reason to be- so small indeed, even where the species is large, as barely lieve it occasionally does. Eschscholtz was convinced that to admit Entomostraca of a very small size. In Charybdæa, what Péron took for internal air-bladders were only ap- which was believed to be agastric, M. Milne Edwards has pendages to the gastric cavities, into which air had been shown that a mouth and an internal cavity with which that introduced by accident upon removing the animals from the mouth is connected actually exist. The projection of extremely delicate tissues hanging from the roof, so to speak, Nervous System and Senses.-We are not aware of any of the funnel-shaped cavity of Charybdæa surrounded a quite satisfactory demonstration of a nervous system in the central mouth and a stomach, from which proceeded four Acalephans. Dr. Grant indeed (Zool. Trans., vol. i.) notices long canals leading to the tapering filaments pendent from a structure in Cydippe which in his opinion can only belong the margin of the animal's body, and these canals he believes to that system; but Eschscholtz, whose labours in investi- to bear analogy to the radiating vessels in Rhizostoma. gating the organization of this class were not small, failed to There is a group of small cylindrical sacs at the beginning discover nerves in the largest which he examined. That they of each canal and opening into it, which, he thinks, may be enjoy sight has been a question. Ehrenberg has endeavoured regarded as biliary organs. The experiments of Spallanzani, to show that Medusa aurita possesses eyes in the form of which were principally made on Aurelia phosphorea, Lam. small red points visible on the surface of the eight brown (Pelagia, Esch.), showed him four groups of convoluted masses which are round the circumference of the umbrella; membranous tubes, which resembled in structure the inand he has compared these so-called eyes to those of certain testines of the Vertebrata, and though he did not trace Rotifera and Entomostraca. He considers the glandular their connections, he seems to have viewed them as true body at the base of the pedicle to be an optic ganglion, and parts of the alimentary canal. They exhibited a peristaltic notices its connection with two filaments that decussate motion both when in the water and out of it, and this moabout the middle of their course; and he views these as tion could be increased by stimulus. Professor Owen sugconstituting part of a nervous circle situated, for the greater gests that these must have been the ciliated and plicated part of its extent, directly along the bases of the row of ten-tube-like testes, or ovaria, according to the sex of the intacles surrounding the umbrella, and so forming a sort of dividuals examined. outer wall of the circular vessel or appendage of the intes tinal cavity which runs round the margin of the umbrella. He also describes another nervous circle, formed of four ganglion-like masses. These he states to be disposed round the mouth, and to be each connected with a corresponding group of tentacles.

But the general opinion seems to be that touch is the only sense possessed by the Acalephans, as far as proof has hitherto gone. That they are sensible to light, though the evidence in favour of their possessing sight properly so called may not be deemed conclusive, will be generally admitted. It is said that some of the smaller tribes have been known to shun a bright light, and to sink into deep water to avoid it. We remember to have seen off Seaton in a calm a shoal of the great Rhizostoma of our coasts swimming high with the tide as they neared our boat, over whose side we were looking, they gradually sank in the clear glassy sea; and it required some dexterity to catch even one or two of the great numbers that passed with the boat-hook, the only engine we had for their capture. The least motion seemed to alarm them. We have observed a similar care in avoiding strange objects, when watching the shoals of a smaller species of Medusæ coming up with the tide in the river Hamble in Hampshire, which is also very clear on the flood-tide when the rains have not been heavy.

The chief seat of the touch appears to be in the tentacula and cirrhi with which the majority of Pulmograda are furnished. Many of them, as we have ourselves observed, make no sign when wounded extensively in the umbrella or disk. That their irritability is not small, is however shown by the experiments of Spallanzani, who, by friction of the muscular membrane of the umbrella and pricking it, excited the contracting and dilating motions in Medusa which had been deposited in a dry place for four and twenty hours, had entirely ceased to exert their ordinary movements, and had lost two-thirds of their bulk or nearly so by the draining out of their contained fluids.

Food and Digestion. The food, small fishes and marine animals, both living and dead, is probably conveyed to the mouth not only by the tentacles and cirrhi with which the greater part of the Medusa are furnished, but also by contractions in the umbrella or disk itself. This must, one should think, be the case in those genera, Eudora for instance, which are without tentacles. The mode of taking the prey does not however seem to be accurately known. Botta's observations were confined to the digestion of a small fish by a Medusa, but he did not see the Medusa catch it. Fishes of some size have been found dead and entangled in the tentacles of Medusa, killed most probably by that benumbing or stinging quality which has obtained for them the name of Sea-Nettles.

By the investigations of M. Milne Edwards principally, we now know that all the Pulmograda have gastric cavities, but all have not mouths in the ord,nary acceptation of the

A good deal of obscurity still hangs over the Respiration and Circulation of the Pulmograda; but we cannot forbear to call attention to two most striking and beautiful examples of the anatomical skill of John Hunter, which may help the observer in his inquiry as to how these animals breathe. In the Physiological Series of Comparative Anatomy in the museum, the foundation of which was laid by him, will be found the following preparations (Series I. Aeration of the blood by means of gills):--No. 982. A Medusa (Rhizostoma cærulea, Cuv.) injected, with a portion of the disk removed so as to expose the central cavity or stomach, and the common orifice by which the numerous nutritive canals of the ramified processes pour their contents into that cavity. The vessels which proceed from it to ramify and subdivide, so as to form the respiratory network in the margin of the disk, are successfully injected. No. 983 shows a portion of the margin of the same specimen. The colour of the vermilion, which some chemical change has destroyed in the preceding preparation, is here preserved. The vascular network is seen to be formed by the lateral ramifications of straight vessels diverging to the circumference of the disk, and placed about an inch apart from each other. The vessels at the central margin of the network are the largest, and encroach in a semicircular form upon the intervals of the straight vessels, before these begin to distribute their lateral branches. The peripheral or terminal vessel of the network is very minute, and follows the scolloped contour of the margin of the disk. The whole of this vascular network is placed on the surface of the disk, which, in the natural position of the animal, rests upon the water; and thus this simple but beautiful respiratory apparatus is most effectually brought in contact with that element, through the medium of which the circulating fluids of the Medusa are submitted to the influence of the atmosphere. (Cat. Mus. Coll. Chir., vol. ii.)

Till lately nothing comparatively was known of the Ge neration of this curious tribe. Gaede, Müller, Eschscholtz, Milne Edwards, Ehrenberg, Jæger, Siebold, and Wagner have all thrown light upon the subject, but the last has satisfactorily proved that some of the Pulmograda at least are dioecious; that they are in fact male and female; and that the organs of the male are in August crowded with spermatozoa aggregated in minute spiriform groups. No copulation has been observed, and the probability is that the male influence is conveyed by dispersion through the ambient medium. The ova are excluded by compression of the sac, and Siebold has traced their stages with as great exactness as has been employed in tracing those of any other animal. Not the least curious part of the generative system and economy of the Pulmogrades is the marsupial apparatus in certain species, as the Medusa (Cyanæa) aurita. This consists of a series of small flask-shaped processes developed from each side of the oral tentacles, where the ovaria are crowded with the impregnated ova, and by a transition, of

which the nature is as yet as problematical as the passage of the embryo into the pouch of the Marsupialia, the ciliated ova, or gemmules, of the Medusa are transferred from the ovaria to the brachial marsupial sacs, and there undergo their development. The young Meduse quit the marsupial pouches in the form of certain ciliated Infusoria, and afterwards assume the form of an eight-armed Polype, before their final metamorphosis, which would seem to take place in the month of February or early in March. The marsupial sacs are deciduous, and disappear soon after the escape of the young.

In the preparation No. 2235, in the Museum of the Royal College of Surgeons, is shown a Medusa (Cyanea aurita, Cuv.). The four circular opaque white bodies in the substance of the disk, and seen in the interspaces of the oral tentacula, are the gemmaria, or organs in which the reproductive ciliated gemmules are developed each gemmary opens by a separate ciliated orifice in the ventral or inferior surface of the body. (Cat. Mus. Coll. Chir., vol. iv.) Some idea of the swarms of Medusa which are occasion

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ally met with may be formed from the note appended to the account of the small luminous Medusa brought from the Red Sea, and preserved in the Museum of the College of Surgeons (Preparations of Nat. Hist. in Spirit), No. 73 A. Henry Salt, Esq., was the donor, in 1811, and the note states that they were in such profusion, that the proportion of Medusa to the water was fully one-third, perhaps nearly one-half. They were luminous only when alive.

ARRANGEMENT.

From the causes above noticed, when observing on the difficulty of satisfactorily examining and preserving the Pulmograda, the distinction of species becomes no easy task; and there is yet another reason, namely, the probability that in most of them the young after its exclusion from the ovarial sac undergoes a series of metamorphoses before it attains its full development, as it certainly does in some.

The names of Péron and Lesueur stand prominent as those of zoologists who have grappled with this obscure branch of natural history; but, as Cuvier observes, in their 'Prodromus' genera often occur which they have established on the authority of the bad figures of inaccurate authors, such as Baster and Borlase, and without having themselves seen the subjects; and from the same cause they have beyond measure multiplied the species. Still their arrangement should be that principally consulted by the student.

The method of Eschscholtz, who paid attention to a consideration hitherto comparatively disregarded, namely, the ramifications of the digestive canal, contains several new genera, which are disposed in a manner entirely different from the arrangement of Péron and Lesueur. The following table will exhibit his systematic distribution of the Medusa :

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Genera: Eudora, Berenice.

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From these two systems, or at least by intercalating among the spectator; c, view of the lower side.

a, view of the upper side; b, in profile, or with the edge of its disk toward

P. C., No. 1182.

VOL. XIX.-R

M. de Blainville remarks that he only knows this genus from the characteristic and short description given by Peron and Lesueur. He doubts whether this Medusa has not a mouth; for he thinks that the centre of the reunion of the four large trunks of the canals ought to be regarded as a stomach. He further inquires whether the individual figured was complete. He says that M. Lesueur informed him that there was a membrane on the lower surface, and he inquires whether this was not perhaps some remains of the stomachal cavity.

Cuvier united this genus with the Geryonia. Eschscholtz places it, as we have seen, in his family Berenicida, and unites Euryale with it.

Charybdæa.

Generic Character.- Body hemispherical, subconical, or even semi-elliptical, furnished on its circumference with foliaceous subtentacular lobes, hollowed below by a great stomachal excavation with an aperture as large as itself. Example, Charybdæa periphylla (Pér. and Les.).

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Tima flavilabris,

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Favonia Octonema,

Lymnorea triedra.

a, the disk seen from above. Section V Pelagia.

Generic Character-Body subhemispherical, lobated, auriculated, furnished on its circumference with a few tentaculiform cirrhi; eight inferior apertures at the extremity of a fistulous? peduncle provided with four very strong and foliaceous arms. Four ovaries. Stomach with cæciform appendages.

Example, Pelagia Labiche, Esch. (Cyan. Labiche, Quoy and Gaim.).

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Generic Character.-Body circular, hemispnericai, lestooned and provided with at least twenty-four tentaculiform

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Chrysaora lutea.

a, fourth of the disk or umbrella seen from below; b, disk without its aprendages.

Rhizostoma Cuvieri,

FOSSIL IMPRESSIONS OF MEDUSA?

Mr. Babbage, in his paper On Impressions in Sandstone resembling those of Horses' Feet,' December, 1836, in which he noticed those in the channel of a stream on the extensive moor called Pwll-y-Duon, about seven miles from Merthyr Tydvil, to which his attention was drawn by Mr. Guest of Dowlais, and the analogous casts in the old red-sandstone of Forfarshire, there called Kelpies' feet, described some observations recently made by Mr. Lyell, on impressions left by Medusa on the rippled sand near Dundee. On removing the gelatinous body of the animal, a circular space was exposed, not rippled, but having around half the border a depression of a horse-shoe form. These marks however were not considered by Mr. Lyell as identical with those called Kelpies' feet, but merely so far analogous as to invite further observations, and to make it desirable to possess drawings of the impressions which different species of Medusa leave when thrown by the tide upon a beach of soft mud or sand. (Geol. Proc., vol. ii.)

PULMONELLA. [SYNOICUM.]
PULMONELLUM. [ZOOPHYTARIA.]

PULP is a name given in vegetable physiology and botany to such parts of plants as are semifluid. This substance appears to the naked eye as a mucilaginous unorganised mass of the nature of a secretion; but it is in reality composed of very thin-sided cells which have little power of cohesion, and secrete in their interior a greater abundance of fluid than is usual. Pulp may therefore be regarded as young and imperfectly formed tissue filled with the secretions peculiar to the species. It is also in some cases, perhaps in all cases, mixed with an abundance of cinenchyma, or laticiferous tissue, which passes through it in all directions in the form of the most delicate ramifications. The pulp of Generic Character.-Body circular, hemispherical, pro- the grape affords a good example of this. To the naked vided on its circumference with lobes or festoons intermin- eye it appears to be nothing more than a fleshy homogenegled with auricles, largely excavated below, with four semi-ous mass that may be compared to half-consolidated gum; lunar orifices, produced by four roots of insertion of a considerable pedunculated mass, afterwards divided into eight very complex brachideous appendages furnished with fibrillary suckers, without a median prolongation. Four ovaries, in the shape of a cross. Stomachal cavity very large and vascular at its circumference.

Rhizostoma.

Example, Rhizosioma Cuvieri.
Habitat.-European Seas.

M. de Blainville separates the genus into two divisions.

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but under the microscope it is found to be a congeries of oval transparent bags turgid with fluid and very easily ruptured; treated with iodine, they lose their transparency in some measure, and acquire a brown colour, when their limits become very distinct. The same re-agent stains still browner the vessels of the latex, whose course and position are thus brought clearly into view. In a few minutes however the colouring fades away in the latter, till they become as indistinct as they were before the iodine was applied: it is therefore necessary that the observation should be made as soon as the iodine has seized upon the latex or its tubes.

PULPIT. This term affords a striking instance of the great change of meaning and application which words frequently undergo, for, exclusively of the Latin termination, it is identical with Pulpitum, which signified that part of the Roman stage (distinguished from the orchestra) on which the actors recited and performed their parts. The French Pupitre and the English Pulpit both come from the same

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