VITAL CAUSES OF CHANGE.

279

CHAPTER X.

Coral Animalcules.

36 Deep in the wave is a coral grove,

Where the purple mullet and gold-fish rove,
Where the sea-flower spreads its leaves of blue,
That never are wet with falling dew,

But in bright and changeful beauty shine,
Far down in the green and glassy brine."

Percival.

We now enter upon a most interesting branch of our subject, the influence of organic action in producing change, and we will soon find that of all agents which at the present moment are forming rocks, the most remarkable are those minute and fragile ani. mals termed Coral Animalcules. A vast number of islands in the Pacific, Indian, and Atlantic oceans are entirely composed of the calcareous skeletons of these minute animals, and they are at the present moment rapidly increasing in their extent. Straits and seas, once easily and safely navigable, are now rendered extremely dangerous, and even impassable. It will not be unprofitable or uninteresting to devote a short space to the consideration of these wonderful specimens of organic existence.

The nature of coral animalcules is but little understood by most persons, they suppose that the hard calcareous substance called coral, is a part of the animal itself, this, however, is not the case. The stony substance, may be compared to an internal skeleton, for it is surrounded by a soft animal investment, capable of ex*panding, and when alarmed, of contracting and drawing itself almost wholly into the hollows of the hard coral. Though often beautifully colored in their own element, yet when taken out of the water they appear like a brown slime spread over the stony nucleus. The coral animalcules exist in a great variety of forms

and of various sizes, some of them are so minute that they cannot be seen without a microscope. They are congregated together like other zoophytes, each individual being connected to a com mon body, so that what is received by any one goes to the nourishment of the whole. The stony matter, or hard substance of the zoophyte, is formed as are the bones and nails in man, by secretions from the animal substance, by which they are penetrated and invested. The cells of the coral, therefore are not built up by the polypi, as they are called, in the same manner as the waxen cells of the bee. We may often observe little patches of yellowish calcareous matter on sea-weed, or shells thrown upon the shore, this upon examination appears to be a kind of delicate net-work, but when examined with a microscope the substance is found to be full of pores, and if the examination is made while the flustra or calcareous matter is immersed in the water, each pore will appear to be the opening of a cell, whence issues a tube with several long arms or feelers; sometimes these expand, and then suddenly close and are withdrawn into the cells, then issue forth again. Thus each individual of the group occupies its own particular cell, but the whole constitutes one family of polypes connected by a common integument, or fleshy or gelatinous substance which invests the whole. Figure 1, of the wood-cut below exhibits the series of cells of the flustra, systematically

arranged. Each cavity is the receptacle of a polype shown with the tenlacula, or feelers, expanded in fig. 2, and contracted into its cell in fig. 3. These views are from drawings made by Mr. Lister, and figured by Dr. Mantell, in his excellent "Wonders of Geology." The animals just described are members of the same

family by whose secretions vast reefs of coral rocks are formed, and mountain masses of calcareous matter produced. They belong to the order Coraliferi, or coral-making, and the class Polypi of Cuvier's Animal Kingdom. The mode of increase of the polyparia is very remarkable. If the flustra just referred to, be carefully watched, a small globule will be observed to be thrown off from the mass, and attaching itself to the sea-weed or rocks, will become the germ of a new colony of this compound animal, as it increases in size it will exhibit upon closer inspection the usual characteristics of the flustra, and if the gelatinous or jellylike substance is removed, a small spot of calcareous matter will be found. The stony secretions of the coral forming animals, appears upon examination to be of the same character as that of shells; some specimens appearing of the same composition as the pearly shells, and others the same as the enamelled shells. In form and color there is condiderable diversity. Our limits will only permit us to give figures of several of the different species, without a lengthened or minute description. The most common varieties of corals, which compose the coral reefs and banks, are the following, according to Lamarck. The Meandrina, or brain. stone coral, which derives its name from the meandering cells, and its general appearance, which resembles the brain, as figured below. Figure 1, represents the animal as seen alive in the sea,

the polypi are retracted or concealed, it is of a reddish or fawn color. Fig. 2 is the coral as it appears when divested of its gelatin. ous covering. This zoophyte sometimes attains the size of four feet in circumference. The base of the Meandrina is firmly attached to the rocks with which it soon becomes identical: as each

successive fleshy mass expires, a new one appears, which gradually expands and deposits its calcareous secretions upon the old one, and thus vast beds of stony matter are accumulated in the bottom of the sea, and become the foundations of coral reefs and islands.. 66 We may compare" observes Mr. Lyell, "the operation of these zoophytes in the ocean to the effects produced on a smaller scale upon the land by the plants which generate peat. In the case of the Spagnum, (page 204), the upper part vegetates while the lower portion is entering into a mineral mass, in which the traces of organization remain, when life has entirely ceased. In corals, in like manner, the more durable materials of the generation that has passed away, serve as the foundation on which living animals are continuing to rear a similar structure." The Caryophilla, or branched star-like coral, is another common species. We give an engraving of an American specimen as it appears when alive. The three branches, each

common and extensive species of coral, fig. 1, represents the

coral as seen alive in the sea, the polypi are of a dark green

appearance. Fig. 2, is a The tentaculae, or arms, The appearance of these

color, and about half an inch in length, protected by deep laminated polygonal cells one-sixth of an inch wide; fig. 3, represents the coral with the animal removed, its name astrea or star-like, is derived from its radiated or starry magnified view of one of the polypes. are seen arranged around the mouth. animals alive, and in activity, is most beautiful when viewed in tranquil water. The surface of the rock appears like a living mass, presenting a great diversity of appearance and color. The Madrepore, or branched cellular coral, is well known, being perhaps the most common species. It will be immediately recognized upon inspecting the figure we have given below. In some

species after the fleshy investment perishes, the little cells appear very numerous as in the figure. The white branched corals usually seen in collections belong to this genus. In the water, the Madrepores are invested with fleshy integuments of various colors and each cell is furnished with its own polype. We have now enumerated the several species of zoophytes most active in the formations of reefs. The stony secretions of all these, when bleached by the action of moisture and light, are of a dazzling whiteness. There is however, a species of coral, Corallium rubrum, or red coral, the stony secretion of which is a bright red color, very beautiful and susceptible of a high polish. A specimen of this coral is here figured. It consists of a brilliant red stony axis invested with a fleshy or gelatinous substance of a pale