The peculiar structure of these wonderful little communities may perhaps be made more intelligible by the aid of a few illustrations. Figure 4 exhibits the branching skeleton and, at the extremities of the branches, the several Polyps by whose vital action the skeleton has been constructed. Some of the animalcules are shown in a state of activity, with their tiny arms spread out in search of food: others are withdrawn within their cells, and appear in a state of repose. This species of Zoophyte, which is highly magnified in the figure, flourishes abundantly on the shores of Ireland and England. It has received the name of Campanularia, from the bell-like form of its cells. Our next cut represents a Gorgonia from the Mediterranean, which is also considerably magnified. The fleshy integument of this specimen is of a brilliant red color: the Polyps are arranged in rows on each side of the stem, and are shown in a state of expansion. [Illustration: Fig. 6.--Frustra Pilosa.] [Illustration: Fig. 7.--Madrepora Plantaginea.] A mass of Coral animalcules, which are known by the name of Frustra Pilosa, is represented of the natural size in Figure 6. To the naked eye it seems like a piece of fine net-work, disposed around a fragment of sea-weed, which may be observed protruding in the upper part of our illustration. With the aid of an ordinary magnifier the net-like surface is seen to abound in minute pores arranged with much regularity. Each of these pores is the cell of a Zoophyte. And if a fragment of Frustra be examined with a powerful microscope, when immersed in sea-water, the curious little inhabitants themselves may be seen darting in and out of their cells, expanding and contracting their long feelers, and exhibiting altogether a wonderful activity. In the adjoining woodcut, Figure 7, is shown another interesting species of the arborescent Zoophyte. It belongs to the family of Madrepores, and abounds in almost all Coral Reefs. Alive under water it appears clothed in a gelatinous coating of rich and varied hues. But when removed from its native element this gelatinous coating, which is the living animal substance, quickly melts away; and, in some instances, runs off from the calcareous skeleton in a kind of watery slime. [Illustration: Fig. 8.--Corallium Rubrum.]