« AnteriorContinuar »
FOSSIL REMAINS OF POLYPES.
It was stated in our Chapter on Strata of the Transition Series, that some of their most abundant animal remains are fossil Corals or Polyparies. These were derived from an order of animals long considered to be allied to marine plants, and designated by the name of Zoophytes; they are usually fixed, like plants, to all parts of the bottom of the sea in warm climates which are not too deep to be below the influence of solar heat and light, and in many species, send forth branches, assuming in some degree the form and aspect of vegetables. These coralline bodies are the production of Polypes, nearly allied to the common Actinia, or Sea Anemone of our own shores. See PI. 54. Fig. 4. Some of them, e. g. the Caryophyllia, see PI. 54. Figs. 9, 10. are solitary, each forming its own independent stem and support; others are gregarious, or confluent; living together on the same common base or Polypary, which is covered by a thin gelatinous substance, on the surface of which are scattered tentacula, corresponding with the stars on the surface of the coral, (see PI. 54. Fig. 5.)
Le Sueur, who observed them in the West Indies, describes these Polypes, when expanded in calm weather at the bottom of the sea, as covering their stony receptacles with a continuous sheet of most brilliant colours.
The gelatinous bodies of these Polypes are furnished with the power of secreting carbonate of Lime, with which they form a basis of attachment, and cell of retreat. These calcareous cells not only endure beyond the life of the Polypes that secreted them, but approach so nearly to Limestone in their chemical composition, that at the death of the Polype they remain permanently attached to the bottom Thus one generation establishes the basis whereon the next fixes its habitation, which is destined to form the foundation of a farther and continual succession of similar constructions, until the mass, being at length raised to the surface of the sea, a limit is thereby put to its farther accumulation.
The tendency of Polypes to multiply in the waters of warm climates is so great, that the bottom of our tropical seas swarms with countless myriads of these little creatures, ever actively engaged in constructing their small but enduring habitations. Almost every submarine rock, and submarine volcanic cone, and ridge, within these latitudes, has become the nucleus and foundation of a colony of Polypes, chiefly belonging to the genera Madrepora, Astrea, Caryophyllia, meandrina, and Millepora. The calcareous secretion of these Polypes are accumulated into enormous banks or reefs of coral, sometimes extending to a length of many hundred miles; these continually rising to the surface in spots where they were unknown before, endanger the navigation of many parts of the tropical seas.*
If we look to the office these Polypes perform in the present economy of nature, we find them acting as scavengers of the lowest class, perpetually employed in cleansing the waters of the sea from the impurities which escape even the smaller Crustacea; in the same manner as the Insect Tribes, in their various stages, are destined to find their food by devouring impurities caused by dead animal and vegetable matter upon the land.f The same systemtude of the universe. We are more perplexed in attempting to comprehend the organization of the minutest Infusoria,*
* Interesting accounts of the extent and mode of formation of these Coral Reefs may be found in the voyages of Pcron, Flinders, Kotzebue, and Becchy; and an admirable application of the facts connected with modern Corals to the illustration of geological phenomena has been made by Dr. Kidd in his Geological Essay, and by Mr. Lyell in his Principles of Geology, 3d edit. vol. iii.
t Mr. De la Beche observed that the Polypes of the Caryophyllia Smithii (PI. 54, Figs, 9, 10, 11,) devoured portions of the flesh of tishes, and also small Crustacea, with which he fed several individuals at Torquay, seizing them with their tentacula, and digesting thern within the central sac which forms their stomach.
* Among the Corals of the Transition Series arc many existing genera, and Mr. De la Bcche has justly remarked (Manual of Geology, p. 454) that wherever there is an accumulation of Polypifers such as would justify the appellation of coral banks or reefs, the genera Astrea and Caryophyllia are present; genera which arc among architects of coral reefs in the present seas.
A large part of the Limestone called Coral Hag, which forms the elevated plains of Bullington and Cunmer, and the hills of Wytham, on three sides of the valley of Oxford, is filled with continuous beds and ledges of petrified corals of many species, still retaining the position in which they grow at the bottom of an ancient sea; as coral banks, are now forming in the intertropical regions of the present ocean.
The same fossil coralline strata extend through the calcareous hills of the N. W. of Berkshire, and N. of Wilts; and again recur in equal or still greater force in Yorkshire, in the lofty summits on the W. and S. W. of Scarborough.
* Ehrenberg has ascertained that the Infusoria, which have hertofore been considered as scarcely organized, have an internal structure resembling that of the higher animals. He has discovered in them muscles, intestines, teeth, different kinds of glands, eyes, nerves, and male and female organs of reproduction. He finds that some are born alive, others produced by eggs, and some multiplied by spontaneous divisions of their bodies into two or more distinct animals. Their powers of reproduction are so great, that from one individual (Hydatina senta) a million were produced in ten days; on the eleventh day four millions, and on the twelfth sixteen millions. The most astonishing result of his observations is, that the size of the smallest coloured spots on the body of Monas Termo, (the diameter of which is only , J__
of a line) is 1__ of a line, and that the thickness of the skin of the sto
mach may be calculated at from „^.fflrff to „0 J^ of a line. This skin must also have vessels of a still smaller size, the dimensions of which are too minute to be ascertained. Abhandlungen der Academic der Wissenschaften zu Berlin, 1831.
Ehrenberg has described and figured more than 500 species of these Animalcules; many of them are limited to a certain number of vegetable infusions; a few arc found in almost every infusion. Many vegetables produce several species, some of which are propagated more readily than others in each particular infusion. The familiar case of the rapid appearance and propagation of animalcules in pepper water will suffice to illustrate the rest.
In the London and Edin. Phil. Mag. Aug. 1, 1836, p. 158, there is an extract of a letter sent by M. Alexander Brongniart from Berlin to the Royal Academy of Sciences of Paris, announcing that Ehrenberg has also discovered the silicified remains of Infusoria in the stone called Tripoli (Polierschicfer of Werner,) a substance which has been supposed to be formed from sediments of fine volcanic ashes in quiet waters. These petrified Infusoria from a large proportion of the substance of this kind of stone from four different localities, on which Ehrenberg has made his observations; they were probably living in the waters, at the time when they became charged with the volcanic dust, in which the Tripoli originated. It is added in this notice that the slimy Iron ore of certain marshes is loaded with Infusoria, of the genus Gallionella.—V'Institut, No. 166.
These most curious observations throw important light on the obscure and long-disputed question of equivocal generation; the well-known fact that animalcules of definite characters appear in infusions of vegetable and animal matter, even when prepared with distilled water, receives &
than that of a whale; and one of the last conclusions at which we arrive, is a conviction that the greatest and most
probable explanation, and the case of Infusoria no longer appears to differ from that of other animals as to the principle on which their propagation is conducted. The chief peculiarity seems to consist in this, that their increase takes place both by the oviparous and viviparous manner of descent from parent animals, and also by division of the bodies of individuals.
The great difficulty is, to explain the manner in which the eggs or bodies of preceding individuals can find access to each particular infusion. This explanation is facilitated by the analogous cases of various fungi which start into life, without any apparent cause, wherever decaying vegetable matter is exposed to certain conditions of temperature, humidity, and medium. Fries explains the sudden production of these plants, by supposing the light and almost invisible sporules of preceding plants, of which he has counted above 10,000,000 in a single individual, to be continually floating in the air, and falling- every where. The greater part of these never germinate, from not falling on a proper matrix; those which find such matrix start rapidly into life, and begin to propagate.
A similar explanation seems applicable to the case of Infusoria; the extreme minuteness of the eggs and bodies of these animalcules probably allows them to float in the air, like the invisible sporules of fungi; they may be raised from the surface of fluids by various causes of attraction, perhaps ever by evaporation. From every pond or ditch that dries up in summer, these desiccated eggs and bodies may be raised by every gust of wind, and dissipated through the atmosphere like smoke, ready to start into life when ever they fall into any medium admitting of their suscitation; Ehrenherghas found them in fog, in rain, and snow.
If the great aerial ocean which surrounds the earth bo thus charged with the rudiments of life, floating continually amidst the atoms of dust we see twinkling in a sunbeam, and ever ready to return to life as soon as they find a matrix adapted to their development, we have in these conditions of the very air we breathe a system of provisions for the almost infinite dissemination of life throughout the fluids of the present Earth; and these provisions arc in harmony with the crowded condition of the waters of the ancient world, which is manifested by the multitudes of fossil microscopic remains, to which we have before alluded. (See Sect. viii. page 290.)
Mr. Lonsdale has recently discovered that the Chalk at Brighton,
Gravesend, and near Cambridge, is crowded with microscopic shells;
thousands of these may be extracted from a small lump, by scrubbing it
with a nail brush in water; among these he has recognised vast numbers