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on closely allied Polyzoa, he has fallen far short of these naturalists in tracing the intermediate course of the alimentary canal. His ideas on this part of the structure seem to correspond very closely with those of Rösel, and he joins with this naturalist in denying the accuracy of Trembley's description of the digestive organs of the “Polype à Panache." He does not admit the existence of distinct muscles, and maintains that Trembley erroneously ascribed retractor muscles to his “Polype à Panache,” asserting that he has mistaken for them the inverted tentacular sheath. Here also, Raspail, in denying the conclusions of Trembley, departs from truth; the celebrated discoverer of the “Polype à Panache” made no such mistake as that attributed to him by Raspail; and though, as we have already seen, he erroneously ascribed to the funiculus the function of a muscle, he interpreted truly as retractor muscles the appearance which Raspail referred to the inverted sheath of the tentacula. Raspail did not allow the cilia with which the tentacula are clothed to escape him, though he strangely refers the phenomena of ciliary motion, here as well as in other cases of its occurrence, to a deceptive appearance occasioned by certain alterations in the density of the surrounding fluid attendant on the act of respiration; an error which we can scarcely otherwise explain than by supposing it to result from the use of a microscope of very inferior powers. He has seen the funiculus which Trembley mistook for a muscle, and attributes to it the function of an ovary; and he has examined the external form of the statoblasts, which he considers to be eggs, and the structure of their investing capsule, with more detail than any previous observer. But the most singular feature in the memoir is to be found in its zoological, rather than its anatomical bearing, for the author refers all the fresh-water Polyzoa to a single species, believing them to be merely different stages of development and non-essential variations of his “Alcyonelle fluviatile;" an opinion which is not very far separated from that of Lichtenstein, already mentioned. The doctrines of Lichtenstein and Raspail, however, made but little way; and it seems, indeed, only necessary to compare the various forms of fresh-water Polyzoa with one another, to be convinced of the entire groundlessness of their positions. Raspail's memoir, upon the whole, though a most elaborate one, and copiously illustrated with well-executed plates, tells us very little of importance, and must, in many respects, be viewed as a retrograde step in this department of zoology. In the same year with the appearance of Raspail's memoir, Meyen published, in the “Isis,' a paper on Alcyonella." He improves, in some important points, Lamarck's definition of the genus, though he retains the incorrect character which ascribes to the animal but twenty or thirty tentacula. He enters also into some anatomical details, but in these we find little new, while they are by no means free from error. He figures more accurately than any other author since the time of Trembley and Baker, the complete course of the alimentary canal, but he mistakes the rectum for the stomach. The chief value, however, of Meyen's memoir is to be found in the announcement of the very important fact, that the Alcyonella produces locomotive ciliated embryos; he figures these, and describes them at length, but his account is in some points incorrect. Raspail, in the memoir already referred to, maintains that the Leucophra heteroclyta, described long since by Müller as an infusorial animalcule, is only a young state of his Alcyonella fluviatilis ; and Meyen now confirms the opinion of Raspail, and shows

* MEYEN, Naturgeschichte der Polypen. “Isis,” 1828.

that Müller's animalcule is really the ciliated embryo of Alcyonella. He admits his inability to determine the nature of the brown egg-like bodies found in the interior of the tubes, and denies to them the office of eggs. In a subsequent note by the same author, published in the “Isis,’ 1830,” he ventures the opinion that the Tubularia sultana of Blumenbach is only the Diffugia proteiformis, a minute Rhizopod now well known, and originally described by M. Leclerc, in a memoir presented nearly forty years previously to the Institut.t In a still later memoir, Meyen informs us that Nordmann has seen crustacea escape from the statoblasts of Alcyonella; and relying on this certainly erroneous observation, he concludes that the statoblasts of Alcyonella and Cristatella are nothing more than parasites peculiar to these genera. In 1828, Dr. Fleming published his ‘History of British Animals.’S In this work he enumerates under the genus Plumatella two species, P. repens and P. gelatinosa, as inhabiting the fresh waters of Scotland. His P. repens is undoubtedly the true P. repens, but his P. gelatinosa is Fredericella sultana. Dr. Fleming has traced the entire course of the alimentary canal, and has recognised in these animals the true polyzoal type of structure. Ehrenberg, in his ‘Symbolae Physicae,’ 1831, defines the genus Alcyonella, but this definition embraces the different species of Plumatella, as well as a new Polyzoon which he had"discovered in the neighbourhood of Berlin, but which he must have observed very imperfectly, for its structure is so peculiar as to place it even in a family distinct from that of Alcyonella, with which he associates it, under the name of Alcyonella articulata. Gervais, who subsequently found it at Plessis-Piquet, near Paris, saw the necessity of characterising it as the type of a new genus, to which he gave the name of Paludicella." In 1837, Mr. William Thompson, of Belfast, discovered this interesting Polyzoon in Lough Erne, in the county of Fermanagh; and it has since been found in abundance in other localities in the British Islands, and on the Continent. At the meeting of the British Association for the Advancement of Science, held at Edinburgh, in 1834, Sir John Graham Dalyell” describes, under the names of Cristatella mirabilis and C. paludosa, two species of Polyzoa as occurring in the fresh waters of Scotland. His C. mirabilis is undoubtedly the C. mucedo of Cuvier, while his C. paludosa is certainly not a Cristatella at all; and from the description contained in the report of his paper, it is impossible to identify the animal so designated. He gives, on the whole, a very good description

* MEYEN, Nachträgliche Bemerkungen zur Naturg. der Polypen des siissen Wassers. “Isis,” 1830. t Leclerc, Sur la Difflugia, nouveau genre de Polype amorphe. ‘Mém. du Museum,’ tome ii, p. 474. f MEY EN, Beiträge zur Zoologie gesammelt auf einer Reise um die Erde, p. 180. “Nov. Act. Nat. Cur.,’ 1834. § FLEMING, ‘An History of British Animals, exhibiting their descriptive characters.’ Edinburgh, 1828. | EHRENBERG, ‘Symbolae Physicae; seu icones et descriptiones animalium,’ &c. Berol., 1828– 1831. * GERVAIs, Recherches sur les Polypes d'eau douce des genres Plumatella, Cristatella, et Paludicella. “Ann. Sci. Nat.,’ 2° sér., vii, p. 74. ** DALYELL, On the propagation of certain Scottish Zoophytes. ‘Rep. Brit. Assoc.,’ 1834.

of his Cristatella mirabilis. He has observed the epistome, and accurately describes the statoblasts, which he has seen to open for the escape of the young. In 1834, M. De Blainville published the first edition of his ‘Manual of Actinology.” In this he constitutes a distinct sub-class of his Polypiaires, under the name of Polypiaria dubia for such as have the tentacula borne upon two diverging arms, in the form of a horseshoe. It includes the fresh-water genera then known, namely, Cristatella, Plumatella, and Alcyonella, together with the Difflugia of Leclerc.—an animal in no way related to them—and the marine genus Dedalaea, established by Quoy and Gaimardt for a very singular animal discovered by these naturalists in the seas of the Mauritius, and with which we are but very imperfectly acquainted. De Blainville's location of the Dedalata in his Polypiaria dubia is founded on the examination of a specimen brought home by Quoy and Gaimard, and preserved in spirits, and the genus is certainly incorrectly associated with the fresh-water forms. In subsequent editions of his ‘Manual, M. De Blainville alludes to the locomotive embryos described by Meyen, but cannot bring himself to admit the correctness of this observation. In 1835, M. Dumortier published, in the ‘Dulletin de l'Académie de Bruxelles, a memoir on the “Polype à Panache" of Trembley. This Polyzoon, which had been previously confounded with Alcyonella and Plumatella, was believed by Dumortier to be sufficiently distinct to render it the type of a new genus, which he accordingly constitut;d, under the name of Lophopus. In consequence of using lenses of too low a power, Dumortier persuaded himself of the absence of cilia on the tentacula, and made this supposed fact the principal character in his new genus. Notwithstanding, however, the erroneous observation on which Dumortier thus relied, the separation of the “Polype à Panache” from the other fresh-water Polyzoa was an important step, and is fully borne out by its general structure. The memoir of Dumortier is chiefly valuable as giving us the most complete account of the anatomy of the Polyzoa which had up to his time been published. To him is due the honour of having been the first to demonstrate a distinct nervous system in these animals; and he describes the cutaneous, circulatory, respiratory, manducatory, digestive, muscular, and reproductive systems, with much detail, and with a correctness which makes us the more surprised that he should have committed so grave an error respecting the tentacular cilia. In the ‘Bulletin Zoologique' of the same year, M. Gervais gives an analysis of the memoir of M. Dumortier, and contends against the right of the “Polype à Panache” to assume the position of a distinct genus, insisting on its being nothing more than a Plumatella. In the year 1837, M. Turpin read before the Royal Academy of Sciences at Paris a memoir on Cristatella. He had received, a short time previously, from M. Gervais, certain minute seed-like organic bodies, which this naturalist had discovered in the Canal d'Ourque, in the city of Paris. M. Turpin, suspecting them to be the ova of some aquatic

* DE BLAINville, ‘Manuel d’Actinologie et de Zoophytologie.” Paris, 1834. + Quoy et GAIMARD, ‘Zoologie du Voyage de l’Astrolabe.’ Paris, 1830-33. : DuMoRTIER, Recherches sur l’Anatomie et la Physiologie des Polypiers composés d'eau douce. ‘Bull. Acad. Brux., ii, p. 422. § TuRPIN, Etude microscopique de la Cristatella mucedo. “Comptes rend. de l'Acad. Sci. Paris,” Jan., 1837; and ‘Ann. Sci. Nat.,’ 2° sér., vii, p. 65.

animal, placed one of them in water, and, after some weeks, had the pleasure of seeing escape from it a minute polypoid animal, which he recognised as that figured and described by Rösel, and afterwards, under the name of Cristatella, assumed as the type of a new genus by Cuvier. Turpin describes the bodies from which these little animals proceeded with considerable detail, but his account is in many respects erroneous. He alludes to the annulus with which they are surrounded, but sets this appearance down as the result of an optical deception, and he incorrectly describes their curious hooked spines as, for the most part, growing from the extreme margin; while he tells us that the bodies in question open in a plain perpendicular to the two faces, to allow of the escape of the young one, instead of having the plane of dehiscence, as is really the case, parallel to the faces. He is at first at a loss to explain how such formidably armed “eggs” could be brought forth with impunity, and he asks: “Quelle pouvait &tre la malheureuse mêre condamné à contenir et surtout à pondre des Ceufs aussi horriblement herissés de crochets?” He afterwards, however, finds an explanation of the difficulty, for seeing the faeces expelled in the form of oval masses, he mistakes these masses for eggs, and thence concludes that the eggs are at first free from spines, and acquire this armature only after being laid. M. Turpin gives a very beautiful figure of the young animal, which he describes with great care, though, not having the advantage of adult or of sufficiently numerous specimens, his account is in some respects erroneous. The same year, M. Gervais published another memoir on the fresh-water Polyzoa." In this memoir he constitutes a distinct genus, under the name of Paludicella, for Ehrenberg's Alcyonella articulata; and he further makes an important step in the classification of the Polyzoa, dividing them into two subordinate groups, Polypiaria hippocrepia and Polypiaria infundibulata, the former being constituted for those with the tentacula upon the margin of a horseshoe-shaped disc, and including all the fresh-water species except Paludicella and Fredericella (= Tubularia sultana, Blumenbach), which, in consequence of having the tentacula arranged on a circular disc, Gervais unites with the marine Polyzoa, to constitute the group Polypiaria infundibulata. We have already seen that De Blainville was impressed with the necessity of this division, and established his Polypiaria dubia, corresponding with Gervais's P. hippocrepia, to meet it; but De Blainville's group, including certain animals which are manifestly incorrectly placed there, required the revision introduced by Gervais. Gervais now corrects the erroneous description of the egg (statoblast) given by Turpin, but he tells us no new fact of importance concerning the animal, and he commits the serious error of uniting all the other species with crescentic discs under the single one of Plumatella campanulata, About the same time, M. Turpin read to the Academy of Sciences a memoir on certain microscopic organized bodies which he found enveloped in some varieties of opal. t. In these, he recognises so much similarity with the statoblasts of the Cristatella, with whose study he had just been engaged, that he does not hesitate to consider them as the eggs of some nearly allied animal. The fossils, however, thus attempted to be determined by Turpin, have nothing

* GERVAIs, Recherches sur les Polypes d'eau douce des genres Plumatella, Cristatella, et Paludicella. “Ann. Sc. Nat.,’ 2° sér., vii, 1837.

t TURPIN, Analyse ou Etude microscopique des different corps organisés et autres corps de nature diverse qui peuvent accidentellement se trouver envéloppés dans la pâte translucide des Silex. ‘Acad. Sc. Paris, Mars, 1837.

to do with the Polyzoa. There can be little doubt that they are the fossil sporangia of certain Desmidieae. In the ‘Transactions of the Philosophical and Literary Society of Leeds,’ 1837, we have a paper by Mr. Teale, on Alcyonella stagnarum.* The author gives a good account of the habits and external characters of the animal; but he informs us of no new fact concerning its anatomy. In 1838, Johnston published the first edition of his excellent “History of British Zoophytes;’t in the account, however, here given of the fresh-water Polyzoa, this author merely follows his predecessors. He distributes the species under the three genera of Cristatella, Alcyonella, and Plumatella ; he makes the “Polype à Panache” merely one of the varieties of Alcyonella stagmorum, and, led astray by the erroneous synonymy of previous authors, he enumerates the Plumatella gelatinosa of Fleming’s “British Animals” as a species with circular disc, distinct from Blumenbach's Tubularia sultana. In the ‘Bulletins de l'Académie Royale de Bruxelles’ of the following year, M. Van Beneden published a note, containing observations on some of the fresh-water Polyzoa.t Nordmann had just indicated the existence of male and female individuals existing separately in Tendra zostericola, a marine Polyzoon,S and M. Van Beneden now makes a similar statement with respect to Alcyonella. | He describes also a circulation of fluid in various parts of the body, and he supposes it due to the action of cilia, which he affirms to exist on the exterior of the alimentary canal as well as on the skin. This motion of the fluid in the interior had been, as we have seen, already noticed by Trembley; and M. Van Beneden now for the first time refers it to its true cause by showing its dependence on vibratile cilia, though he incorrectly describes the external surface of the alimentary canal as ciliated. He believes he has seen at the base of each tentacle an aperture, which he regards as an aquiferous mouth (“bouche aquifere”), destined to give admission to the external water; though in a subsequent memoir he admits that this appearance is deceptive. He describes the great supraOesophageal ganglion, and mentions the existence of locomotive ciliated embryos in Alcyonella. He mentions having found, along with M. Gervais, the Fredericella and Paludicella; and in fine he shows how the form of Alcyonella is varied by accidental circumstances influencing its growth. In the same year, M. Gervais published, in the “Annales Françaises et Etrangères d'Anatomie,' a valuable paper on the fresh-water Polyzoa." This memoir, which is an extension of his previous one, is of more importance in a zoographical than in an anatomical point of view. For Blumenbach's Tubularia sultana, he institutes a new genus under the

* TEAle, On Alcyonella stagnarum. ‘Trans. Phil. Soc. of Leeds,’ i, p. 116.

f Johnston, ‘History of the British Zoophytes.” Edinburgh, 1838.

f VAN BENEDEN, Quelques Observations sur les Polypes d'eau douce. “Bull. Acad. Brux.,’ 1839.

§ NordMANN, Recherches microscopiques sur l'anatomie et le développement du Tendra zostericola. ‘Ann. Sci. Nat.,’ 2° ser., xi.

| With Van Beneden's statement of the separation of the sexes in Alcyonella, my own observations do not agree. See above, p. 32.

"I Gervais, Observations sur les Polypes d'eau douce. ‘Annales Françaises et Etrangères d’Anatomie,’ 1839.

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