This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
Zoophytes of old Authors. Phytozoa (Ehrenberg).
(111). It is not surprising that many members of the extensive class upon a consideration of which we are now entering should have been regarded by the earlier naturalists as belonging to the vegetable kingdom, with which, in outward appearance at least, numerous species have many characters in common.
(112). Fixed in large arborescent masses to the rocks of tropical seas, or, in our own climate, attached to shells or other submarine substances, they throw out their ramifications in a thousand beautiful plant-like forms. Incrusting the rocks at the bottom of the ocean with calcareous earth separated from the water which bathes them, they silently build up reefs and shoals, justly dreaded by the navigator and sometimes giving origin, as they rise to the surface of the sea, to islands which the lapse of ages clothes with luxuriant verdure and peoples with appropriate inhabitants.
(113). Among the calcareous structures derived from the tropical seas, usually known by the general terms Madrepores, Corals, etc, and which, from the beauty of their structure, form the ornaments of our cabinets, few are more common than those denominated Fungiae and Meandrinae - animals belonging to the group Madrephylliaea of systematic zoologists.
(114). These masses consist of thin plates or laminae of calcareous matter (fig. 23), variously disposed in different species, but in the Fungia agariciformis, which we have selected as an example, radiating from a common centre, and forming a circular mass resembling a mushroom. When living in its native element, every part of the surface of this stony skeleton was incrusted with a layer of animal jelly, dipping down into the interstices of the plates, and covering the whole framework. In the figure, the darker portion indicates the living crust.; whilst from the lighter parts it has been removed, to show the stony skeleton itself. There are no arms or moving parts adapted to the prehension of food, and no separation of organs for the performance of the vital functions; the thin membranous film apparently absorbs the materials of its support from the water of the ocean, and deposits within its substance the calcareous particles which it secretes, moulding them into the form peculiar to its skeleton, which it gradually enlarges as its own extent increases.
Fig. 23. Fungia agariciformis.
(115). The gelatinous investment, however, gives certain dubious indications of vitality, and possesses a power of contraction so as to retire between the laminae of its skeleton when roughly handled, and thus conceal itself from injury. Upon the surface of the soft crust are seen a number of vesicles (indicated in the figure), which have been regarded as rudimentary tentacula from the circumstance of their being-able to contract and vary their dimensions; recent observations, however, lead to the belief that they are cavities filled with air, serving an important purpose in the economy of the creature - namely, that of preventing it from being turned upside down by the occasional agitation of the ocean. These air-vessels may therefore be looked upon as floats, which, rendering the upper surface more buoyant than the inferior, materially assist in preventing such an accident.
(116). The reproduction of Fungia is effected by the development of sprouts or gemmae which pullulate from the animal substance as buds issue from a plant, and remain for some time fixed to the parent by a species of foot-stalk, which sustains them until they have attained to a considerable size, - the young Fungiae being upwards of an inch in diameter before they become detached. "When mature, they separate from the top of the stony peduncle which hitherto supported them; and at this time the skeleton of the young Fungia, when divested of its fleshy part, shows a circular opening beneath, through which the radiating plates of the upper surface are visible. In a short time a deposit of calcareous matter takes place, which cicatrizes the opening, the marks of which, however, can be traced for a considerable period.
(117). In the earliest period of its development, the foot-stalk by which the young is united to the parent, as well as its radiating disk, is entirely enveloped with the soft parts of the animal; but as the upper portion spreads, and assumes its characteristic form, the pedicle is left naked, and the gelatinous coating extends only to the line where the separation afterwards takes place.
(118). It is generally supposed that the calcareous matter forming the skeleton of these madrepores is perfectly external to the living crust that secretes it, and accordingly is absolutely extra-vital and removed from the future influence of the animal. Such a supposition is, however, at variance with the facts above stated, and incompatible with many circumstances connected with the history of the lithophytous polyps. On trying to detach the soft envelope from the surface of the skeleton, the firmness of their adherence would render such a want of connexion improbable - they appear to be, as it were, incorporated with each other; and, besides, the separation of the Fungia from the peduncle whereby it was joined to the parent Fungia during its earlier growth necessarily supposes a power of removing the calcareous par- ' tides after their deposition. It is therefore demonstrable that the earthy matter secreted by the polyp is deposited in the tissue of its substance, and still remains, in a greater or less degree, subject to absorption and removal; of this, however, we shall have fuller evidence hereafter.
The compound polyps consist of a mass of gelatinous matter, which indicates, by its power of contraction upon the application of stimuli, a degree of sensation, and of a great number of polyps, or flower-like mouths, which spring from the surface of the common body, and are individually capable of seizing and digesting prey, the nutriment thus gained being appropriated to the nourishment of the general mass.