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1820. Plumatella cristata. Schweigger, Handbuch der Naturg., p. 424.
Iconography—The original figures are those of Trembley, Baker, Shaw, Dumortier, and Van Beneden.
HABITAT-In ponds and ditches, where it attaches itself to the submerged parts of Lemna, Sparganium, and various other aquatic plants, avoiding exposure to bright sunlight.
Localities.—British : Abundant in a millpond near Little Baddow, Essex; a pond in the Zoological Gardens, Dublin; abundant. G. J. A.—In the water by the side of the Willow-walk, Chelsea, and in various waters in the neighbourhood of London. Shaw. Foreign: Holland. Trembley.—Belgium. Dumortier and Van Beneden.
When removed from the water, L. crystallinus appears immersed in a transparent gelatinous investment which envelopes the entire colony, leaving only the orifices free. This investment, which, as has been already shown,” is really a delicate transparent membrane filled with a fluid and representing the ectocyst, may be easily removed; and, indeed, specimens kept for some time in confinement may often be found quite freed from it. I cannot help thinking that the specimens observed by M. Van Beneden, and described by this naturalist as destitute of the investment in question, were only accidentally in this state, which I believe is never presented by freshly captured, healthy individuals.
* Wide supra, p. 14.
Full-grown specimens have the endocyst deeply lobed, so as to cause it to present a kind of palmate appearance. The intervals of the lobes, however, are nearly filled by the gelatinoid ectocyst. Young specimens are not lobed, and then they correspond to the “Bellflower Animal" of Baker. Both Baker and Van Beneden ascribe to this animal a power of locomotion. To the existence of this power, however, my own observations are opposed; the colony is certainly very easily detached, and will when all is quiet again readily fix itself, so that a passive change of place may in this way be effected; but though I have had numerous specimens constantly under my eyes, I have never witnessed anything like the active locomotion of Cristatella. The ectocyst is perfectly colourless and transparent, the endocyst and polypides are pale brownish-yellow. The statoblasts are larger than those of any other fresh-water Polyzoon, except Cristatella. They are of an elliptical form, with the long diameter prolonged at each extremity into a short acute point. L. crystallinus is one of the largest of the Polyzoa, and this circumstance, together with the transparency of the coenoecium, renders it peculiarly well adapted for examining the structure of the class. In many cases the perigastric space in Lophopus was found to contain numerous spherical bodies (Pl. II, figs. 16–23), which floated freely in the perigastric fluid, where they were rapidly whirled about under the influence of the currents. They varied much in size, some being about the Town of an inch in diameter, while others were as large as an ordinary Wolvoa. globator. Some were seen to consist in a spherical transparent cell, with nearly colourless granular contents, involving numerous minute spherical bodies, apparently young cells; these contents were aggregated on the inner surface of the wall, where they constituted a thick, somewhat irregular layer. In other cases the contents were seen to be entirely resolved into a brood of young cells, which completely filled the parent-cell; while in the largest individuals these secondary cells might themselves be seen in various stages of growth and subdivision, some presenting the appearance of a little spherical granular mass with visible nucleus, but without distinct cell-wall, others somewhat larger, with the cell-wall become distinct, and others in which the granular contents had retired from the cell-wall towards the centre of the cell, where they were to be seen surrounded by a colourless fluid. In a still further stage the contents had become divided into two masses, while in still more advanced cases each of these masses might be seen again dividing into two others, the subdivision being preceded by the appearance of two nuclei in each mass. The whole of this brood of young cells was ultimately liberated by the rupture of the large parent-cell, and then floated away in the perigastric fluid. That the bodies now described had no necessary connection with the Polyzoon in whose
interior they occurred, must, I think, be admitted; their presence is, without doubt, purely parasitical.
Name.—A diminutive noun, formed from Alcyonium, a genus of marine Actninozoal
The animal originally described by Pallas, under the name of Tubularia fungosa, and by Bruguière under that of Alcyonium fluviatile, was assumed by Lamarck as the type of a new genus which he named Alcyonella; but, deriving its characters from the very incorrect description and figures of Bruguière, Lamarck's definition of the genus is necessarily erroneous,
Some naturalists insist on the identity of the genera Alcyonella and Plumatella, and go so far as to maintain that the animal described under different names, by Pallas, Bruguière, and Lamarck, possesses no essential character to distinguish it even specifically from P. repens or P. campanulata, the difference being solely the result of accidental causes—especially the form and size of the object to which it is attached—operating on it during its growth, and thus influencing its development. The author who has most elaborately defended this view is M. Raspail, and a similar opinion has been advocated by Ehrenberg and Siebold. After, however, much attention to the subject, I have satisfied myself that there are sufficient grounds for keeping the two groups generically distinct. It is quite true that, in its young state, Alcyonella has its tubes distinct, creeping along the surface of the supporting body, and in this condition, I admit that it cannot be distinguished from a Plumatella, but it is only in its early youth that it presents this form. Plumatella, on the other hand, preserves a distinctness of its tubes throughout its whole existence. I have found very large specimens of Plumatella under precisely the same circumstances as those in which we meet Alcyonella, and yet without the slightest tendency to assume the form of the latter genus. Another argument, which strongly supports the view here taken, is derived from the fact that Alcyonella has not yet been detected in Ireland,” though Plumatella repens is exceedingly abundant throughout the island, frequently presenting the utmost luxuriance, and yet invariably preserving a total distinctness of its tubes, no matter what the form or size of the object on which it grows.
In distinguishing the species of Alcyonella, I have employed characters drawn chiefly from the general habit of the animal, the structure of the coenoecium, and the shape of the statoblasts. We have seen, in the anatomical section of this monograph,t that the ectocyst in the genera Alcyonella and Plumatella sometimes presents upon its surface the appearance of a transparent longitudinal furrow running along the length of each tube, commencing in the vicinity of the orifice as a triangular notch-like space, and passing into a prominent keel as
* In my Synopsis, published in the “Annals of Natural History,’ 1844, I recorded Alcyonella stagnorum as a native of Ireland. The animal, however, there alluded to under this name is really the Polype à Panache; and I was led into this error from adopting at that time the opinion of Raspail, Johnston, and other naturalists, that Trembley’s animal was identical with the A. stagnorum of Lamarck.
+ Wide supra, p. 13.
it recedes from this point. The presence of the longitudinal furrow constitutes an important specific character, and its value is enhanced by its being of easy application; it occurs in two out of the three species of Alcyonella.
Another very valuable character is obtained from the shape of the statoblasts. The ordinary or free statoblasts, both in Alcyonella and Plumatella, present two different shapes; in some species they are broadly elliptical, the diameters of the ellipse being to one another pretty nearly in the ratio of 2:3; in others again they are narrow, the diameters being nearly as 1:2. The terms broad and elongated therefore, as applied to the ova in the following diagnosis, are to be understood as expressing this difference of shape.
Generic character.—Coenoecium composed of membrano-corneous branched tubes, which adhere to one another by their sides; orifices terminal. Statoblasts elliptical, with an annulus but without marginal spines.
Number of known species three.
1. Alcyonella fungosa, Pallas. Pl. III.
Specific character.—Coenoecium fungoid, formed of numerous branched vertical tubes destitute of a furrow. Statoblasts broad.
SYNoNYMs.—1768. Tubularia fungosa. Pallas, Descript. Tub. Fung. Nov. Comment. Acad. Sci. Imp. Petropol. tom. xii, p. 565, tab. 14. (Original figures.) 1782. Spongia lacustris. Schmiedel, Icones Plantarum et Anal. Partium. 1786. Leucophra heteroclita. Müller, Animal. Infusor. p. 158, tab. 22, fig. 27-34. - (Locomotive embryo, original figures.) 1789. Alcyonium fluviatile. Bruguière, Encyc. Méth. 1789, p. 24, pl. 472, fig. 3. (Original figure, bad.) 1802. Alcyonium fluviatile, Bosc. Vers. vol. iii, p. 132. 1816. Alcyonium fluviatile. Lamouroux, Pol. flex. p. 354. 1816. Alcyonella stagnorum. Lamarck, An. sans Vert. 1st edit. vol. ii, p. 102. 1820. Alcyonella stagnorum. Schweigger, Handbuch der Naturg. p. 423. 1821. Alcyonella stagnorum. Lamouroux, Exposit. Méth. p. 71, tab. 76, fig. 5-8. (Figures copied from Bruguière.) 1824. Alcyonella stagnorum. Lamouroux, Enc. Méth. 1824, Zooph. p. 38. 1828. Alcyonella fluviatilis vel A. ultimus evolutionis gradus. Raspail, Hist. Nat. de l’Alcyonelle fluv., Mém. de la Soc. d’Hist. Nat. de Paris, tom. iv, p. 130, pl. 12-16. (Original figures.) 1828. Alcyonella stagnorum. Meyen, Isis, tom. xxi, p. 1225, pl. 14. (Original figures.) 1831. Alcyonella stagnorum. Ehrenberg, Symbolae Physicae Evert. Dec. 1, Pol. fol. a. 1834. Alcyonella stagnorum. Blainville, Man. d’Actin. p. 491, pl. 85, fig. 8. (Figure copied from Raspail.)
1835. Alcyonella stagnorum. Carus, Tabulae Illustrantes, pars 3, tom. 1. (Figure
Iconography.—The original figures are those of Pallas, Müller (embryo), Bruguière, Schmiedel, Raspail, Meyen, Teale, Johnston, Van Beneden (Bull. de l'Acad. de Brux., 1839), Van Beneden (Mém. de l'Acad. de Brux., 1848), Dumortier and Van Beneden (Hist. Nat. des Pol. Comp.), Dalyell.
HABITAT.—Stagnant and slowly running waters, canals, &c., attaching itself to stones, floating timber, and submerged branches of trees; loving obscure places.
Localities.—British: Regent's Canal, London, attached to the sides of the docks, abundant; Chelmar Canal, Essex, abundant. G. J. A.—London and East India Docks, on the Thames, attached to floating timber, abundant. Mr. Busk, Mr. Quekett, Mr. Bowerbank, and G. J. A.—In brackish water, near Ipswich. Mr. Wigham.—Near Leeds. Mr. Mathewman.—Berwickshire. Sir J. Graham Dalyell.—It is, probably, generally distributed through England. No Irish locality.
Foreign.—France. Bruguière, Raspail, Gervais-Belgium. Van Beneden (Bull. de l'Acad. de Brux.) Dumortier and Van Beneden (Hist, Nat. des Pol, comp.)—Germany, Meyen.—Russia. Pallas.