The pedicles are in general of a conical form, and not unfrequently flattened. milar. By grinding the globular part as well as the pedicle on Texture of both parts sia stone, he discovered that their texture appeared to be similar, and that by the frequent ramifications of the fibres, of which their substance was composed, a net work was. formed, not much unlike the parenchyma of vegetables. We therefore perceive that a loose resemblance, sufficient to excuse the vulgar opinion of their origin, is observable between these bodies and the terrestrial fruits. These bodies, like fruits, appear to have been formed chiefly of a parenchymatous substance; their pedicle seems to answer to the ftalk; whilst the opening on their superior part agrees with what is termed the eye of fruits. But a little atten- Its difference tion shews that, unlike to the parenchyma of fruits, which from that of is formed of vessels terminating in minute points, the substance of these bodies is formed of a species of net-work, which, as M. Guettard observes, if all the matter contained within the meshes could be removed, would resemble a skain of thread, of which one part, answering to the pedicle, is pinched together, and the other, answering to the body, is spread out without being cut. Again, the eye, in fruits, is not pervious, as is that part which answers to it in these fossils; nor does the pedicle at all agree with the stalk of fruits, either in proportionate size, or in figure. fruits. fig: Scheuchzer describing a fossil of this kind refers it to the Fossil supposalcyonium stupposum Imperati*; but of the identity of ed to be a seathese substances Mons. Guettard, with much propriety, doubts; although he allows that the external form, and particularly the opening in the upper part, might readily lead to this supposition. This doubt arose in the mind of M. Guettard, from comparing the ftructure of one of the alcyonium stupposum of Imperatus with the description of its structure as given by John Bauhin and by Count Marsilli; the result of his comparison being, that both the descriptions were in some respects erroneous. Taught by careful examination, he states it to be composed of fibres, more or less fine, intersecting each other, without order or Lithograp. Helvet. P. 15. regularity, The sea-fig a sponge. Difference between this and the fossil. Fungites, or trified mush regularity, and anastomosing together by their ramifica tions, by which they form irregular meshes of various figures and quite empty. By this contexture a spongy mass is formed, which is covered by a thin pellicle, constituted in the same manner, excepting that the texture is more close and compact, and extended into a membrane-like substance, which may be detached and easily raised from the body, and which, when examined by a lens, appears to be a mass of fine fibres forming very small meshes, similar to the large ones of which the body is composed. The foot stalk, which spreads out and is a species of basement by which the fig is attached to the body on which it grows, does not seem to differ from the general substance in its conformation. Hence M. Guettard concludes the sea-fig to be merely a sponge, differing from other sponges only in form, and possessing like them the property of imbibing water and losing it by compression. On comparing the structure of the sea-figs with that of these fossils, M. Guettard points out differences which are undoubtedly very essential. In the pedicles of the fossils, he observes that circular points may be seen, which will be found to be continued into the spherical part of these bodies; so that by different transverse sections they may be traced, passing on like so many veffels, from the pedicle into the substance, and even on to the surface of the fossil: whereas, in the sea-fig, the fibres have no such regularity of disposition, nor are they thus continued like tubes from the pedicle into the subftance of the fig. M. Guettard next describes the other kind of fossil, supposed pe- which belongs to the class of fungites, and which, like the ficoid fossils just treated of, are open at their superior and wider part, and in general possess somewhat of a conical form and from their varying in length, width, and size, frequently bear a resemblance to cups, glasses, funnels, cones, &c., whilst others are longer, cylindrical, and even fusiform. This variety of figure is frequently dependant on the circumstances of the fractures which they have suffered; these fossils, like the former, being rarely found in a perfect state. M. Guettard appears to have been entirely foiled in the attempt to discover any recent zoophyte, which might be considered as bearing any analogy with these fossils, He first was disposed to consider them as being similar to the spongia elegans of Clusius, or the spongia dura of Sloane, but this opinion he found reason to relinquish, and was then induced to believe that they bore a nearer resemblance, in their general characters, to some species of madrepores than to any of the sponges. In several of these fossils he discovered an outer layer, which appeared to differ from the general substance of the fossil; and his opinion, he thought, derived support from this circumstance, for, on examining the interior lamina of these fossils, he conceived that it much resembled the hard smooth part which forms the corresponding parts in madrepores, &c. Madrepores and corals, he observes, are covered by a substance which has been distinguished as their cortical part, and immediately beneath this, there is a smooth substance of very close and compact texture, in which there are no striæ nor traces of any fibres. With this latter substance, he thinks, the external layer of these fossils exactly agrees: and he is confirmed in the supposition that it originally belonged to them, and was not derived from the matrix in which they lay, by observing that, in one specimen, several little flat shells of oysters were adhering to this surface. Baltic. Nothing, he thinks, in the fossil kingdom approaches so Single starred near to these fossils, as the single-starred corals of the corals of the Baltic, described by Fougt. The only difference, M. Guettard remarks, is that the corals described by Fougt have ftriæ which extend from the centre of the coral to the edge, in such a manner as to form a star. This difference is however sufficient to remove all idea of similarity between the two bodies; since, as we have already seen, the star constitutes the genus Madrepora, to which those corals belong, whilst in the fossil bodies now under consideration, there exist none of the characters which mark any of the species of zoophytes, which we have hitherto examined. Many of these fossil bodies, it will be seen, differ so much from any known recent zoophyte, that were it not that vaft numbers of these muft be concealed from us, in the numerous recesses of the ocean, they would be concluded to possess not the leaft resemblance with any animal substance now exifting; indeed, so considerable is that difference, Many fossils apparently of unknown ge nera. Difficult to distinguish alcyonia from recent state. difference, that some substances will be placed before you, which, not only cannot be referred to any particular known species, but which would almost authorize the formation of new genera for their reception. We shall proceed, however, as nearly as possible, according to the generally accepted systematic classification; and shall derive what aid can be obtained, from the examinations which have been made of living substances apparently of a similar nature. It is intended, therefore, to endeavour to comprise, under the genus alcyonium or spongia, the substances so accurately inquired into by M. Guettard, as well as several others which have not been spoken of by him, but are evidently of the same kind. With respect to the classification of these bodies, a difficulty almoft insuperable presents itself; since the chasponges in the racteristic marks by which the substances belonging to these two genera are distinguished, in a recent state, are frequently not to be discovered after they have sustained the change of petrifaction. Previously, however, to proceeding further in an inquiry on this subject, it will be proper to consider the nature of both alcyonium and of sponge, and to ascertain what are the distinctive characters of each. Characters of The alcyonium is an animal which assumes a vegetable the alcyonia, form, and which is either of a fleshy, gelatinous, spongy, or leathery substance, having an outward skin full of cells, with openings possessed by oviparous tentaculated hydra: the whole substance being fixed to some other body by a seeming trunk or root. More minute ly examined by Donati, Count Marsilli, who carefully examined not only the physical, but the chemical properties of these bodies, observes that they are all surrounded by a porous leather-like bark; and that the interior substance is, in some, a jellylike matter, and in others, a mass of light ash coloured acicular spines, which prick the hands on being handled, in the same manner as do the spines of the plant called the Indian fig. Donati, in his Essay on the Natural History of the Adriatic Sea, has made, in some respects, a more minute examination of the structure of two different species of alcy enia than even that of Count Marsilli, and was able to ascertain by the aid of a magnifying glass, the peculiar forms assumed by the spines of which these animals are in a great measure composed. Of these we shall soon have occasion to speak more particularly. The forms in which these animals exist are very nume- Exist in varirous; this depending not merely on the number of species, ous forms. but on the different irregular forms which the same species under different circumstances may assume. Thus Marsilli observes the same alcyonium, which sometimes grows flat, and thus covers large pieces of rocks, is at other times found in a rounded form. blance to From the different colours as well as forms which some Named from of the species of these substances possess, they have ob- their resemtained names expressive of their resemblance to certain fruits. fruits. Thus the alcyonium lyncurium, being of a globose form, of a fibrous internal structure, of a tubercular surface, and of a yellow colour, has been termed the seaorange the a. bursa being of a sub-globose form, of a pulpy substance, and of a green colour, has been termed the green sea-orange or sea-apple: the a. cydonium, which is of a roundish form, and of a yellow colour, has been distinguished as the sea-quince: and the a. ficus, from a very close resemblance to the fig in its form, has been called the sea-fig. The sponge is a fixed, flexible animal, very torpid, va- Characters of rying in its figure, and composed either of recticulated sponges. fibres, or masses of small spiculæ interwoven together, which are clothed with a living gelatinous flesh, full of small mouths or holes on its surface, by which it sucks in and throws out the water. nature sus The vitality of sponges had been suspected by the an- Their animal cients, even in the time of Aristotle; they having per-pected by the ceived a particular motion in their substance, as if from ancients, shrinking, when they tore them off the rocks. This opinion of their possessing a degree of animal life was also entertained in the time of Pliny. Count Marsilli* confirmed this opinion by observing, on their being taken out of the * Histoire Physique de la Mer. p. 53. and confirmed by the mo derns, sea, |