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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 Dedalæa, established by Quoy and Gaimard † 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 Dedalaa 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 · Bulletin de l'Académie de Bruxelles,' a memoir on the “Polype à Panache ” of Trembley. # This Polyzoon, which had been pre. viously 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 constituted, 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.

I 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 être la malheureuse mère condamné à contenir et surtout à pondre des œufs aussi horriblement herissés de crochets?” He afterwards, however, finds an explanation of the difficulty, for seeing the fæces 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.† 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 Paludi. cella. *Ann. Sc. Nat.,' 2° sér., vii, 1837.

† Turpin, Analyse ou Etude microscopique des different corps organisés et autres corps de nature diverse qui peuvent accidentellement se trouver enveloppés 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 Desmidiee.

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 stagnorum, 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. I Nordmann had just indicated the existence of male and female individuals existing separately in Tendra zostericola, a marine Polyzoon, 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 aquifère ”), destined to give admission to the external water; though in a subsequent memoir he admits that this appearance is deceptive.

He describes the great supra@sophageal 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. † Johnston, ' History of the British Zoophytes. Edinburgh, 1838. I 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.

GERVAIS, Observations sur les Polypes d'eau douce. • Annales Françaises et Etrangères d'Anatomie,' 1839.

name of Fredericella, called in honour of Frederic Cuvier, and he gives a tolerably extensive synonymy of the species of fresh-water Polyzoa, which he distributes under the five genera, Cristatella, Alcyonella, Plumatella, Paludicella, and Fredericella ; he, however, still maintains the generic identity of Lophopus and Plumatella. He divides the whole, as he had done in his previous paper, into two sub-classes, Polypiaria hippocrepia and P. infundibulata.

In the first volume of the Supplement to the Dictionnaire des Sciences Naturelles,' published in 1840, M. Gervais, in the article Alcyonella, again gives us the result of his researches into this subject; he still rejects the generic distinctness of Lophopus, and even views Alcyonella and Plumatella as mere species of the same generic form.

In 1841, M. Coste read to the Académie des Sciences a paper on the organization of the fresh-water Polyzoa ; * though unaccompanied by figures, M. Coste's memoir gives a very good account of most of the important points in the anatomy of the hippocrepian Polyzoa; it describes the muscular, digestive, and nervous systems with much exactness and with considerable detail; and maintains the expediency of removing the Polyzoa out of the Radiata, and dlacing them among the Mollusca.

A few months later, M. Coste addressed to the Académie a short note on the “ Tubulaire sultane” (Fredericella sultana),t in which he announces that the organization of this Poylzoon is in general quite conformable to that of the hippocrepian species described in his former communication.

In the year 1842, MM. Dumortier and Van Beneden read, before the Royal Academy of Brussels, the first of a series of papers, which these naturalists proposed presenting conjointly, on the Compound Polypes of fresh water.' This memoir consists entirely of a historical introduction to the subject; it is most elaborate and learned, and I have derived much assistance from it in drawing up the present historical outline.

In 1843, I read to the Royal Irish Academy a memoir “On the Muscular System of Paludicella and other Ascidian Zoophytes of fresh water.'S The paper is chiefly occupied with the description of the muscles of Paludicella. They are divided into three groups-one belonging to the alimentary canal, one to the tentacular sheath, and one to the walls of the cell. Being then an inexperienced observer, and possessing but an imperfect microscope, I was unable to pursue the anatomy of the animal as far as could be desired, and several interesting points of structure escaped me at the time. The retractor muscles of the alimentary canal in Plumatella repens, and the radiating muscles of its sheath, are also described in this memoir, though I then overlooked the fact that the latter are divisible into an anterior and a posterior set; while Dr. A. Farre's account of the action of certain muscles in the Polyzoa is examined, and an attempt made to explain such action in a manner somewhat different from the views entertained by this anatomist.

* Coste, Propositions sur l'organisation des polypes fluviatiles. “Comptes Rendus,' 1841.

Coste, Observation relative à la Tubulaire sultane. Comptes Rendus,' 1811.

DUMORTIER et Van Beneden, Histoire Naturelle des Polypes composés d'eau douce. Nou. veaux Mémoires de l'Acad. Roy. de Bruxelles,' t. xvi.

§ Allman, On the Muscular System of Paludicella and other Ascidian Zoophytes of fresh water. Proc. Roy. Irish Acad.' 1843.

the genera

In this paper

At the meeting of the British Association for the Advancement of Science, held at Cork, in the same year, I read a paper on Plumatella repens.* In this paper it was attempted to reduce to some sort of order the chaotic accumulation of synonyms by which the species is encumbered. This was facilitated by distinguishing two variations which P. repens is found to assume, according as it grows upon surfaces of small or large extent, and from not attending to which much confusion had arisen; one of these variations is presented in the “ Federbuschpolyp” of Rösel, the other in the “ Kammpolyp” of Schäffer, which Müller afterwards assumed as the form on which he founded his species Tubularia repens. The digestive apparatus was also described, as well as the muscles which act on the alimentary canal and invaginated tunic; it was shown that the latter muscles consisted of two distinct sets, an anterior and a posterior, whose peculiar arrangement was pointed out. On the same occasion I presented to the meeting a short paper, containing a synopsis of

and species of fresh-water Polyzoa occurring in Ireland.t two new species of Plumatella and one of Fredericella are described, and the peculiarities of Paludicella were deemed of sufficient importance to raise this genus to the type of a distinct family among the fresh-water Polyzoa.

In 1846, I described, in a paper read before the Royal Irish Academy, the locomotive ciliated embryos of Plumatella fruticosa ;and at the meeting of the British Association for the same year, presented to that body the result of some observations I had made on the structure of Cristatella. The nervous ganglion of this Polyzoon was described, and the muscular fibre was shown to be striated, and to have a tendency to break into discs. The statoblasts (or the ova, as I then, in common with other observers, believed them to be), were described as enclosed, during their young state, in a ciliated membranous sac, within which the hooked spines, of which they are at first destitute, are afterwards developed.

In the second edition of the History of British Zoophytes,' published in 1847, Johnston subjects the portion of his work which treats of fresh-water Polyzoa to a complete revision, and now distributes the British species under the genera Cristatella, Alcyonella, Plumatella, Fredericella, and Paludicella; he, however, still maintains the specific identity of the “

“ Polype à Panache ” with the Alcyonella stagnarum.

In 1848, we obtain from M. Van Beneden a very valuable memoir on the fresh-water Polyzoa of Belgium. The author here enters into important details of the ana and classification of the fresh-water Polyzoa, and gives excellent descriptions and copious synonyms of the several species. After the lapse of nearly a century, he restores to the Alcyonella staynarum of Lamarck the specific name fungosa originally bestowed on it by Pallas. This is but an act of justice to its discoverer, and ought to be followed by subsequent systematists. Van Beneden also makes the addition of a second species of Alcyonella, whích he describes under the name of A. flabellum.

*

ALLMAN, On Plumatella repens. 'Reports of British Association, 1843.

† Allman, Synopsis of the genera and species of Zoophytes inhabiting the fresh waters of Irelánd. ' Reports of British Association,' 1843 ; and ' Ann. and Mag. of Nat. Hist.,' May, 1844.

| ALLMAN, On the Larva state of Plumatella. • Proc. R. I. Ac.,' 1846.

Allman, On the Structure of Cristatella mucedo. “Reports of British Association,' 1846.

Il Van Beneden, Recherches sur les Bryozoaires Fluviatiles de Belgique. Mém. de l'Acad. Roy. de Belgique,' tome xxi, 1848.

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