Imágenes de páginas
PDF
EPUB

subalpine lakes or of rapid rivulets, where, by close adhesion to the under surface of stones, they avoid the danger of being carried away by the current of the stream ; while others prefer slowly running rivers or the sluggish waters of canals and ponds.

They are almost all light-shunning animals, loving the dark and gloomy recesses of the lakes and rivers they frequent, where they may be found beneath the shade of aquatic plants, or attached to the inferior surface of stones, or lurking under the arches of bridges where a ray of direct sunlight never enters; Cristatella alone delights in exposure to the full influence of the solar beams, and may be seen basking upon the upper side of submerged stones, or creeping over the stems of aquatic plants in the clear waters of lakes and ponds.

With the solitary exception of Cristatella, they are all, in their adult condition, utterly incapable of locomotion, being then permanently attached to some fixed object; Cristatella, however, creeps about on the stones and plants of its native lake, and thus affords the only instance as yet known of a truly locomotive Polyzoon.

Lastly, some are timid creatures, withdrawing into the recesses of their cells on the slightest disturbance, and not again daring to venture forth until a long lapse of time has convinced them that all is once more quiet without ; while others must be roughly handled before they will think of retreating; and the light-loving Cristatella rejoices in the constant exposure of its plumy crown, no ordinary disturbance will force it to retire, it seems altogether incapable of existing, except in the midst of the countless vortices which its ciliated tentacula are for ever whirling around it.

GENERAL GEOGRAPHICAL RANGE of THE FRESH-wat ER Polyzo A.

The number of forms of fresh-water Polyzoa which, after careful comparison, I have deemed it right to retain as distinct species, amount to twenty-one in all. Of these, sixteen are British; and of the remaining five, one has only been described as occurring in the fresh waters of Belgium, while four are confined to the United States of America Of these four American species, two constitute respectively the types of two distinct genera.

We do not, however, as yet possess a sufficient number of observations to entitle us to advance any generalisation of much value as to the geographical distribution of the freshwater Polyzoa. The most northern point at which we have any positive information of the discovery of a species is probably the neighbourhood of Stockholm (Baeck, in ‘Acta Holm., vii, 1745), while the neighbourhood of Nice (Risso, ‘Hist. Nat. de l'Europe Mérid.") would seem as far as is yet known to be the most southern limit of the group in the Eastern Hemisphere, and Philadelphia (Leidy, “Proceed. Acad. Nat. Sci. of Philadelphia, vols. v and vii) to be the most southern limit at which we have any record of a fresh-water Polyzoon having been discovered in the Western Hemisphere. Vlademir, in Central Russia, where Alcyonella fungosa was originally found by Pallas (Pallas, in ‘Nov. Comm. Petr., 1768), is the most eastern point, while Philadelphia (Leidy, l.c.) must for the present be viewed as the extreme limit towards the west. The species, so far as we are as yet acquainted with their distribution, are thus confined to the North Temperate Zone, not one having been recorded as occurring south of the Mediterranean in the Old World, or of Philadelphia in the New. It is by no means improbable that they also exist in warmer latitudes, and we cannot but be surprised that they should have escaped the explorations of the numerous naturalists who have examined the regions lying further towards the tropics. We know that the fresh-water tanks in India have been subjected to examination, both botanically and zoologically; and though we should naturally expect to find the fresh-water Polyzoa luxuriating in such a habitat, none of the naturalists who have described the productions of these reservoirs make any mention of them ; and yet the species of Spongilla which abound there, and whose European representatives are so frequently found associated with Polyzoa, have been made the subject of interesting and elaborate investigations. The United States of America appear to be especially rich in the fresh-water Polyzoa ; and when we bear in mind, that it is but lately that these animals have received the attention of American naturalists, while but a small portion of that part of the world has hitherto been examined with special reference to them, and that nevertheless—though all the European species have not yet been recorded as living there—two entirely new generic types have been brought to light, while many of the species found present a state of luxuriant development of which we know nothing in the Old World,—when we bear in mind all these facts, we can scarcely avoid the belief that North America will yet prove the grand metropolis of the tribe. Further facts must be obtained, before we can arrive at any generalisations of much importance regarding the altitudinal distribution of the Polyzoa. All the British fresh-water species occur in these islands at the level of the sea, and most of them have also been met with in our alpine and subalpine lakes. I have found Plumatella repens and P. fruticosa in Lac Leculejo in the Pyrenees, at an altitude of 4590 feet; and P. repens in Lac d'Aul, another Pyrenean lake, at an altitude of about 6500 feet, which is the greatest elevation at which any Polyzoon has as yet been recorded. The depth at which the fresh-water Polyzoa occur in the waters frequented by them is never considerable. I have met with Plumatella jugalis attached to the long petioles of Nymphaea alba, in the waters of a sluggish canal, at about four feet below the surface; but in most instances, the fresh-water Polyzoa will be found at much less depths, and frequently at the very surface, attached to the under side of floating leaves, or upon the stones at the margin of lakes, where they are exposed to the ripple as it breaks upon the shore.

[ocr errors][merged small]

CoNDENs Ed SYNoPsis of THE ORDERs, SUB-orders, FAMILIES, AND GENERA.

The fresh-water Polyzoa admit of being divided into eight generic groups.

The discri

mination of these is very easy in the living animal; but as some of the genera are founded on the form of the polypide alone, the canacium not presenting one character which can be employed for the purposes of distinction; while in others the form of the entire animal is so changed by death, as to render it almost utterly incapable of conveying any idea of what it had been, we are in most instances obliged to examine the animal in a living state before we can form any safe opinion as to even the genus to which it belongs.

The following is a condensed synopsis of the orders, sub-orders, families, and genera of

fresh-water Polyzoa :

[ocr errors]
[blocks in formation]

C |

<!

H

>

-E |

P- *-
Coenoecium P
C rooted. LUMATELLIDAE.

à f

3 URNATELLEA. - - URNATELLIDE.

H

H

O

3 PALUDICELLEA. - - PALUDICELLIDAE.

>

C

Lophophore
with two
long arms.

Arms of lo-
phophore }
obsolete.

Coenoecium sacciform;
ectocyst gelatinoid ;
statoblasts oval, des- |
titute of spines. J

Lophopus.

Coenoecium tubular,
tubes united ; ec-
tocyst pergamenta-
ceous.

Alcyonella.

Coenoecium o
tubes distinct ; ec-
tocyst pergamenta-
CeOus.

Plumatella.

Fredericella.

Urnatella.

Paludicella.

* For the characters of the Orders and Sub-Orders see Table, p. 10.

5.

DIAGNosis, SYNONYMY, AND NATURAL. History of the GENERA AND SPECIES.

CRISTATELLIDAE. Genus I. CRISTATELLA, Cuvier, 1798. Name.—A diminutive noun formed from crista, a crest, in allusion to its tentacular plume.

The genus Cristatella was established by Cuvier, for the little animal originally described by Rösel under the title of “Der Kleinere Federbusch Polyp mit dem ballenförmigen Körper.” Its characters were given in the ‘Tableau Elémentaire des Animaux,’ published in 1798, and it is the first generic group constituted for any of the fresh-water Polyzoa, hitherto all confounded together in discordant and unzoological associations. Rösel's animal, however, was unknown to Cuvier, except from the figures and descriptions left us by its discoverer; and it was not until Turpin and Gervais many years afterwards rediscovered it, having hatched it from statoblasts found in the Canal d'Ourcq, in the city of Paris, that any additions were made to the original account left us by Rösel. Still, however, nothing was known of the animal but in its young and partially developed state, and it was only afterwards, when adult and fully formed specimens were met with, that the real nature of this beautiful

Polyzoon was properly understood.
The genus, which includes as yet but a single species, may be thus characterised:

Generic character.—Coenoecium sacciform, hyaline, with a common flattened discadapted for locomotion; orifices placed on the surface opposite to the disc, and arranged in several concentric marginal series. Statoblasts orbicular, with an annulus and marginal spines.

Species unica. Cristatella mucedo, Cuvier. Pl. I.

Specific character.—Same as that of the genus.

SyNoNYMs.—1755. Der Kleinere Federbusch-Polyp. Rösel, Insect. Belustig. Supp., p. 559,

tab. 91. (Original figure.)

1766. La seconde sorte de Polypes à Bouquets. Ledermuller, Amusm. Mic. 2" cinq., p. 94, pl. 87. (The figures are imperfect copies from Rösel.)

1798. Cristatella mucedo. Cuvier, Tab. Elém., p. 656.

1816. Cristatella vagans. Lamk., An. sans Vert., 1st edit., vol. ii, p. 97.

1817. Cristatella mucedo. Cuv., Règne A., 1st edit., vol. iv, p. 68.

1820. Cristatella vagans. Schweigger, Handbuch der Naturg. p. 423.

1824. Cristatella vagans. Lamouroux, Enc. Méth. Zooph., p. 226, pl. 472. (Figures copied from Rösel.)

1824. Cristatella vagans. Goldfuss, Naturhistorisch Atlas. (Figures copied from
Rösel.)
1828. Alcyonella, secundus evolutionis gradus. Raspail, Hist. Nat. de l'Alcyon. fluv.,
Mém. de la Soc. d’Hist. Nat. de Paris, vol. iv, p. 129.
1830. Cristatella mucedo. Cuvier, Règ. An., 2d edit., vol. iii, p. 296.
1834. Cristatella mirabilis. Dalyell, Rep. Brit. Assoc., p. 604; and Edinb. New
Phil. Journ., vol. xviii, p. 414.
1834. Cristatella vagans. De Blainville, Man. d’Act., p. 489, pl. 85, fig. 7. (Figure
copied from Rösel.)
1834. Cristatella vagans. De Blainville, Dict. Sc. Nat, art. Cristatelle, fig. 7.
(Figure copied from Rösel.)
1836. Cristatella vagans. Lamarck, An. sans Vert., 2d edit., vol. ii, p. 110.
1837. Cristatella mucedo. Turpin, Ann. Sc. Nat., 2d series, tom. vii, p. 65, pl. 2, 3.
(Original figures.)
1837. Cristatella mucedo. Gervais, Ann. Sc. Nat., 2d series, tom. vii, p. 77, pl. 4.
(Original figures.)
1838. Cristatella mucedo. Johnston, Brit. Zooph., 1st edit., p. 308, pl. 43. (Figures
copied from Turpin.)
1839. Cristatella mucedo. Gervais, Ann. Franç. et Etrang. d’Amat., tom. iii, p. 133.
1840. Cristatella moisissure. Gervais, Dict. Sc. Nat. Suppl., art. Alcyonelle, Planches
Supplémentaires, Pol, fluviatiles. (Original figures.)
1843. Cristatella mucedo. Thompson, Rep. Brit. Assoc., p. 285.
1844. Cristatella mucedo. Allman, Ann. of Nat. Hist., vol. xiii, p. 330.
1846. Crislatella mucedo. Allman, Rep. Brit. Assoc., Trans. of Sect., p. 88.
1847. Cristatella mucedo. Johnston, Brit. Zooph., 2d edit., p. 387, pl. 73. (Figures
copied from Turpin.)
1848. Cristatella mucedo. Van Beneden, Bryoz. Fluv. de Belg., p. 16; Mém. de
l'Acad. Roy. de Belgique.
1848. Cristatella mirabilis. Dalyell, Rare and Remarkable Animals of Scotland,
vol. ii. (Original figures.)

Iconography.—The original figures are those of Rösel, Turpin, Gervais in ‘Ann. Sc. Nat...’ Gervais in “Dict. Sc. Nat.' Suppl., and Dalyell.

HABITAT-In clear lakes and ponds, where it creeps slowly over the upper side of submerged stones and the stems of aquatic plants, delighting in sunlight.

Localities.—British : A millpond near Little Baddow, Essex; Union Canal, Edinburgh ; a beautiful little subalpine lake near Glandore, County Cork; Lakes of Killarney, Grand Canal, Dublin; a lake near Armagh, and several other Irish localities. G. J. A.— Duddingston Loch, near Edinburgh; Coldingham Loch, Berwick; a garden pond at Binns House, Linlithgowshire. Sir J. G. Dalyell.

Foreign : Lake of Lucerne; “Grand Etang,” Fontainbleau. G. J. A.—Near Paris. Gervais and Turpin.—Belgium. Van Beneden.—Germany. Rösel.

The first perfectly developed specimen of Cristatella mucedo was described in 1834, by Sir John Graham Dalyell, who discovered it near Edinburgh, and perceiving it to be so very

« AnteriorContinuar »