I.Zoophytes: including—
1.Porifera, or Amorphozoa: the most simple animal structures; as the Sponges.
2.Polypifera, or Polypiaria; Coral-animals.
3.Bryozoa, or Molluscan Zoophytes; as the Flustræ.
II.Echinodermata, or Echinoderms; Comprising—
1.Crinoidea; or Lily-shaped animals.
2.Asteriadæ; Star-fishes.
3.Echinidæ; Sea-urchins.
III.Mollusca, or Mollusks. Under this head not only the fossil shells of testaceous mollusca, but also those of a lower order of animals, the Rhizopodes, or Foraminifera, will be treated of.
1.Foraminifera.
2.Bivalves: the Lamellibranchia, and Brachiopoda.
3.Univalves: the Gasteropoda and Pteropoda.
4.Cephalopoda; those with chambered shells, as the Nautilus and Ammonite; and the naked tribes, the Sepiadæ, or Cuttle-fish.
IV.Articulata. (Animals protected by a hard jointed envelope or case.)
1.Cirripedia: as the Balanus, or Barnacle.
2.Annelida: red-blooded worms, as the Serpulidæ.
3.Insecta, and Arachnida or Spiders.
4.Crustacea; including Crabs, Lobsters, Trilobites, &c.
V.Pisces; or Fishes.
VI.Reptilia; or Reptiles.
VII.Aves; or Birds.
VIII.Mammalia.
IX.Man.

[CHAPTER VII.]

FOSSIL ZOOPHYTES.—PORIFERA OR AMORPHOZOA—POLYPIFERA OR CORALS—BRYOZOA OR MOLLUSCAN ZOOPHYTES.

Many tribes of the extraordinary beings whose mineralized relics are the immediate subject of our investigation, have largely contributed to the solid materials of which the sedimentary strata are composed. In the most ancient rocks in which vestiges of organic structures have been detected, those of Zoophytes hold a conspicuous place; and in the seas of tropical climates, the agency of the Coral-animalcules, or Polypifera, is producing enormous deposits, and laying the foundations of new islands and continents, and forming reefs of rocks hundreds of miles in extent, which, if elevated above the level of the sea, would rival in magnitude the mountain-chains of modern Europe.

The reader unacquainted with the natural history of these marvellous creatures will find an account of their nature and economy, and of the physical effects produced on the earth's surface by their agency, in the sixth lecture of Wond. vol. ii. p. 588.

The term Zoophytes, or animal-plants, comprises two very distinct classes of living beings, namely, the Porifera, or Sponges, which (if not vegetables) are wanting in many attributes regarded as essential characteristics of the members of the animal kingdom; and the Polypifera, or polype-bearing-animals,—the Corals; which are generally associated groups or aggregations of individuals, united by a common organized mass or axis, each polype having an independent existence, and exhibiting volition and perception, in a greater or lesser degree.

Fossil Porifera.

FOSSIL PORIFERA.

The terms Amorphozoa (signifying animals of variable shapes), and Porifera (structures traversed by pores or channels), are employed by naturalists to designate the Sponges and analogous organisms, which appear to occupy the boundary line that separates the animal from the vegetable kingdom. The true position of the Sponges in the great system of Creation is still a disputed point; for while many distinguished naturalists regard them as Protozoa, or the lowest type of animal organization, others of equal eminence affirm that neither in structure nor functions do they differ from vegetables in any essential particular; and that if a line be drawn between the two kingdoms the Porifera must be placed on the vegetable side of the boundary. On the other hand, Dr. George Johnston, in his delightful work on the British Zoophytes,[193] expresses his opinion that there is nothing to discountenance the belief that these bodies hold an intermediate place; that they are, in fact, the true Zoophytes, or animal-plants; in some forms, as the green Spongillæ of our lakes, the vegetable nature prevails; while in others, as the horny or keratose sponges filled with mucilaginous slime, and the fleshy Tethya whose oscula, or pores, are said to exhibit signs of irritability, the animal character predominates.