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an aquatic stem, and gives a tolerably good view of the expanded plume. He describes and figures the tentacular cilia. He tells us that each tentacle is furnished on the extremity with a depression, which he compares to the nail of the finger. This, however, is evidently the result of an erroneous interpretation of the appearance presented when the curved extremity of the tentacle is turned towards the eye of the observer and fore-shortened. So impressed, however, is he with the resemblance of the tentacle to a finger, that he says the animal may be called “Das Finger-thier,” and he is in great delight at seeing one of the supposed fingers when separated from the plume swimming about with an apparently spontaneous motion.

Dumortier and Van Beneden inform us* that Schmiedel, in his 'Icones plantarum,'describes and figures, under the name of Spongia lacustris, the Alcyonella in the condition in which it is found in the autumn after the soft parts have disappeared. The 'Icones plantarum' was published in 1782. I have not succeeded in procuring it.

In 1786, was published the “Animalcula Infusoria’t of Müller. In this work is described, under the name of Leucophra heteroclita, a minute animal of whose identity with the ciliated embryo of Alcyonella fungosa, as subsequently pointed out by Meyen, or more probably with that of Plumatella repens, there can be now no doubt. Müller's description is accompanied by figures, very good considering the imperfect construction of the microscopes then available.

In 1789, we find Bruguière, in the 'Encyclopédie Methodique,’ describing, under the name of Alcyonium fluviatile, a production sent to him by M. Dantic, who found it in the waters of the fountain of Bagnolet, near Paris. I Bruguière was evidently unacquainted with the memoir of Pallas, but his account leaves us in no doubt of the identity of his Alcyonium fluviatile with the Tubularia fungosa of this naturalist. His figure, however, is singularly incorrect; he represents the animal with a variable number of attenuated filiform tentacula, each terminated by a spherical capitulum, and the whole springing from about seven eighths of the circumference of a circular disc. In his location of the Polyzoon among the Alcyoniums, he errs too, as much as Pallas did when he made it a species of Tubularia.

In 1797, Lichtenstein, believing that he had witnessed certain Polyzoa escaping from the little spherical capsules which occur imbedded in the base of Spongilla, maintained, in a communication to the Natural History Society of Copenhagen, that the fresh-water sponge consisted only of the cells of these Polyzoa after having been abandoned by the polypides ;g an opinion which could only have arisen from some very confused observations, and probably from his having mistaken a dead Alcyonella for a Spongilla. He further maintains that all the forms of fresh-water Polyzoa then known are only variations of one and the same species.

Hitherto, no step of importance had been made towards the scientific classification of the fresh-water Polyzoa. The invention by Linnæus of a binary nomenclature, had, it is true,

* DUMORTIER et Van Beneden, Hist. Nat. des Polypes Comp. d'eau douce. "Nouveaux Mémoires de l'Acad.-Roy. de Bruxelles,' tome xvi, 1843.

+ Otho FRIDERICUS Müller, ' Animalcula Infusoria Fluviatilia et Marina.' Hauniæ, 1786. | BRUGUIERE, ‘Encycl. Method.' Vers, p. 24. § LICHTENSTEIN, "Skrivter of Naturhistorie Selkabet,' p. 104. Kiobenhavn, 1797.

prepared the way for a systematic arrangement; but, as yet, the Polyzoa of fresh water had been placed in the same genera with marine forms of a totally different organization, while some of them had not been accurately distinguished from one another.

At length, Cuvier, in his • Tableau élémentaire des Animaux,'* struck by the distinctive characters of the little Polyzoon described by Rösel, under the name of “Der Kleinere Federbusch-polyp mit dem ballen-förmigen Körper,” assumed it as the type of a new genus, to which he gave the name of Cristatella. The other fresh-water Polyzoa he allowed to remain in the genera in which his predecessors had placed them, and even with regard to his Cristatella, though he acknowledge its affinity with the other fresh-water Polyzoa, he was ignorant of its true relations, for he kept it in the vicinity of the infusorial Vorticellæ.

In the year 1804, Vaucher published, in the · Bulletin de la Société Philomathique,' a short description of two Polyzoa, one of which he believes to be the animal described by Schäffer (Tubularia repens, Müller); the other a new species to which he gives the name of Tubularia lucifuga.† Vaucher's memoir is accompanied by figures of both species, but the description is so meager, and the figures so defective, that it is impossible to determine the species intended.

The memoir of Vaucher was followed by a most important reform. Bosc, already convinced, that the so-called Tubularias of fresh water were incorrectly associated with the marine group of this name,I now constituted for their reception a distinct genus, whose characters he gave in the same number of the ‘Bulletin' as that which contained Vaucher's memoir. The following are the characters on which Bosc founded his new genus :

Polypier fixé à tige grêle, membraneux, souvent ramifié, terminé, ainsi que ses rameaux par un polype dont le corps peut entrer entièrement dans la tige, et dont la bouche est entourée d'un seul rang de tentacules ciliés.”

Bosc, however, though he defined the genus, neglected to name it, and his views received but little attention till Lamarck, in his · Histoire des Animaux sans Vertèbres, published in 1816, gave the name of Plumatella to the genus defined by Bosc; while, for the Alcyonium fluviatile of Bruguière, he constituted a new genus under the name of Alcyonella. In his definition of the genus Alcyonella, Lamarck has evidently been led into error by the description and figures of Bruguière, for the celebrated author of the History of Invertebrate Animals,' though he had seen recent specimens, seems to have examined them very imperfectly, and to have taken for granted the correctness of the account in the 'Encyclopédie.' He describes the polypes as “elongali cylindrici ; tentaculis circa orem 15 ad 20, erectis, fasciculum turbinatum vel infundibuliformem uno latere imperfectum componentibus." To Lamarck, however, notwithstanding the erroneous characters in this definition, is due the credit of having been the first to distribute the fresh-water Polyzoa under three distinct and peculiar genera, namely, Cristatella, Alcyonella, and Plumatella, a most important step towards the further elucidation of the tribe. Lamarck associates Cristatella and Alcyonella with Difflugia, a Rhizopod previously described by M. Leclerc, and with Spongilla, to constitute, under the name of “ Polypiers fluviatiles,the first section of his “ Polypes à Polypier ;"

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* Cuvier, Tableau élémentaire de l'histoire naturelle des Animaux. Paris, 1798.
† Vaucher, Observations sur les Tubulaires d'eau douce. • Bull. Soc. Philom.,' 1804, p. 157.
# Bosc, Histoire Naturelle des Vers.'

while Plumatella is united with Tubularia and Cellaria, and many other marine Hydrozoa and Polyzoa, to form, under the name of Polypiers vaginiformes,” the second section of the same order. Lamarck enumerates four species of Plumatella, namely, P. cristata="

“Polype à Panache,” Trembley; P. campanulata =“Federbusch-polyp,” Rösel; P. repens = Kammpolyp,” Schäffer ; and P. lucifuga, Vaucher.

The specific name of fluviatile given by Bruguière to the only species of the genus Alcyonella, at that time known, was changed by Lamarck into stagnarum, a name certainly more in conformity with the habits of the animal, but one far less expressive than the original name of fungosa given by Pallas, a name which, independently of its appropriateness, ought, in accordance with the rules of priority, and in justice to the memory of Pallas, to be still preserved.

In his · Histoire des Polypiers,'* published in 1816, Lamouroux changes Lamarck's name of Plumatella into that of Naisa, a change entirely uncalled for, and founded on erroneous views of the structure of the genus; and though Lamouroux retains the name of Naisa in his · Exposition Méthodique,'t published in 1821, Deslongchamps is the only other naturalist I can find who has thought it necessary to adopt it. $

With the exception of the observations made by Trembley on his “ Polype à Panache,” when he described a complete alimentary canal and retractor muscles, those by Baker, who gives an exceedingly correct account of the digestive tube in his “Bell-flower animal,” and those by Müller, who correctly describes the same parts in his Tubularia repens, though he has left us no figure, we find, up to the period of which we now write, no remark of any value on the internal structure of the fresh-water Polyzoa. In the year 1828, however, the attention of naturalists was called to the structure of these animals in a most elaborate memoir published by Raspail, under the title of 'Histoire Naturelle de l'Alcyonella fluviatile.'S

Raspail had, a short time before, in conjunction with M. Robineau Desvoidy, presented to the Academy of Sciences at Paris, a memoir on the same animal. This memoir, for a knowledge of which we are solely indebted to Cuvier's report || --for it was never published -contains a most erroneous view of the subject, and maintains that the so-called polypes have no necessary connection with the sponge-like mass of the Alcyonella, and are merely accidental occupants of the cells.

In the second memoir, however, the author entirely abandons his former opinion. This memoir is characterised by much originality, and, like most of the writings of Raspail, is marked by a complete freedom from the restraints which the authority of previous investigators so generally imposes. Many of his observations, however, are evidently made with inferior instruments, and the memoir is full of hasty generalisations, which the author builds on a far too limited number of facts. Raspail has detected the mouth and anus of Alcyonella ; but though he has had the advantage of the previous observations of Trembley, Baker, and Müller,

* LAMOUROUX, Histoire des Polypiers Coralligènes flexibles,' Caen, 1816.
+ LAMOUROUX, ' Exposition Méthodique des genres de l'ordre des Polypiers.' Paris, 1821.
| DESLONGCHAMPS, ' Encyclopédie Méthodique, Zoophytes,' 1824.

§ Raspail, Histoire Naturelle de l'Alcyonelle fluviatile et des genres voisins. "Mém. de la Soc. d'Hist. Nat. de Paris,' iv, 1828.

|| CUVIER, ‘Hist. des progrès des Sci, Nat.,' tome ii.

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 Diflugia 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.' 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 ‘Symbolæ Physicæ,' 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 süssen Wassers. 'Isis,' 1830.

† Leclerc, Sur la Difugia, nouveau genre de Polype amorphe. Mém. du Museum,' tome ii,

p. 474.

I Meyen, 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.

|| EURENBERG, ‘Symbolæ Physicæ; seu icones et descriptiones animalium,' &c. Berol., 1828– 1831.

I 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.,' 1831.

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