In a specimen in the museum, prepared by Hunter, the polypes are seen in situ, and in the small specimen represented by c, Hunter demonstrated the organic basis of the tubes, after removal of the calcareous material by acid. Thin sections of this coral, which is very brittle, occasionally exhibit a cellular structure, with the openings of numerous foramina, and in a specimen I possess, the fibres of a sponge have penetrated some of these foramina, as in the case of the Pinna-shell mentioned in a former Lecture, at page 37. This is a very common circumstance in all corals, and by acting

FIG. 78.

growths.

on thin sections with hydrochloric acid, the calcareous matter is removed and the true nature of the fibres

easily made out; but being familiar with the sponge-fibres, I soon recognized those in the Tubipora as old ac

quaintances. Confervoid

A section of Coral exhibiting confervoid growths also are very frequently met with in the skeleton of corals, as all these bodies possess animal matter, which, decomposing after death, becomes a nidus for the development of confervæ, and hardly a section can be examined without exhibiting such an appearance as that shown in Fig. 78.

LECTURE X.

SKELETON OF ZOOPHYTES.

IN the last order of the class Anthozoa, the Helianthoida, the polypes are single, free or permanently attached; fleshy, naked or encrusted with a calcareous polypidom, the upper surface of which is crossed by radiating lamellæ. The most familiar examples of this order are the Actinia, familiarly known as Sea-Anemonies or Animal Flowers, some species of which are common on all parts of our coasts. In certain states of the atmosphere, especially when the weather is stormy, the Actinia appear as conical masses of fleshy substance, but when the sea is calm and the sun bright, they expand themselves, and then they resemble beautiful flowers; their tentacula disposed in one or more circles and beautifully coloured, are very like the petals of a flower. The Actinia mesem

bryanthemum, in particular, which is very common on the coast of Sussex, has a row of large tubercles of a most splendid blue colour, like lapis-lazuli, on the outside of the tentacula. These animals live a very long time, and it is said that the late Sir John Dalyell kept some of them alive for upwards of twenty years by giving them fresh sea-water nearly every day. The external or cuticular coating of the Actinia is thin and coloured, the inner or corium, thick, leathery, and more or less white; the inferior surface is flattened to form a discoid base, or foot. Some species are covered with tubercles, others have numerous pigment spots scattered irregularly on their outer surface.

A vertical section of the entire animal, as shown in Fig. 79, exhibits a circular perforation, the mouth,

FIG. 79.

a

A, vertical section of an Actinia showing its internal structure. a, spicula from the tubercles magnified 250 diameters. b, tentacula. c, tubercles between the tentacula.

surrounded by the coloured tentacula, b, leading to a flask-shaped stomach, which, instead of occupying the entire cavity of the body, as in the Hydra, is suspended within that cavity by a number of vertical septa, forming a corresponding number of cavities, or chambers, which contain the ovaries

and testes. The cavities

for the lodgment of the

ovaries are large, and situated near to the external tunic; those for the testes are smaller, and in immediate contact with the coats of the stomach. The upper part of all the septa is perforated, so that each chamber communicates not only with those adjoining, but also with the interior of the tentacula, each of which, as shown at b, is tubular and perforated at its free extremity, so that water taken into the chambers is propelled, by the contraction of the walls of the chambers, into the tentacula, distending them, and by this means causing their protrusion and the expansion of the entire animal.

200

The microscope reveals to us no trace of calcareous or siliceous skeleton in these animals, with the exception of spicula in certain tubercles, c c, which occur in some species between or external to the tentacula. These spicula, as shown at a, are of nearly equal size, measuring on the average th of an inch in length, and pointed at both extremities. Professor Bailey, of New York, who discovered them, believed that they were composed of silica, like those of the sponges; but as they are destroyed by a red heat and not acted on by acids, it is more probable that they consist of horny matter. The Actiniæ subsist for the most part on small crabs and other crustacea that come within the reach of the tentacles; they do not appear to move to any extent in search of their prey, being generally fixed to the rock by the discoid sucker on their inferior surface. The soft parts of the food are rapidly digested,

while the indigestible portions are rejected by the mouth, there being but a single opening to the stomach, from which viscus the nutriment is directly absorbed. For the purpose of better securing the animals that they seize, the tentacula are said to be furnished with poison vesicles and spicula, somewhat similar to those in the Hydra; if the finger be placed in contact with the tentacula of most of the common species of our shores, a stinging sensation will be felt.

The Actinia are propagated by ova, which are developed in the lobulated glandular ovaries situated in the interseptal chambers, and impregnated by the sperm-cells of the twisted testicular tubuli also seated in the same chambers. The ova, after fertilization, are said to remain in the interseptal chambers, and the young Actiniæ escape by the mouth of the parent, but it is still uncertain how they find their way into the stomach. It is equally certain that the Actinia occasionally, although unfrequently, propagate by gem

mation.

During a visit to Brighton last year, I had the opportunity of verifying this statement, having seen as many as five or six young Actiniæ adhering to the base of a full-grown animal, from which they subsequently separated, and attached themselves to the sides of the glass jar in which they were kept. Like the Hydræ, they possess the power of reproducing lost parts, and when one of them is divided into two or more pieces, each part is capable of becoming a perfect animal. The