Both belong to a Division in the Animal Kingdom which is well above the level of jelly-fishes. Both have arms or rays, proceeding from a central disc. But in the starfish the rays are separated; in the sea-urchin they are joined together. Starfishes and sea-urchins are able to move and even to travel, though in most cases with extreme deliberation. Both can put out little tube-feet suckers, by means of which they can change their position, and can even slowly right themselves, when turned the wrong way up. Sometimes the sea-urchin uses its sharp spines as an additional means of getting along. And while the common starfish can seldom advance faster than at a rate of about one half-inch per minute, there is a species which flings itself forward in a more reckless and rapid style, by using its rays as limbs. Starfish and sea-urchin are alike protected by an armour of hard little plates, arranged in neat rows upon the skin. Not plates made in a workshop, and purchased by the owner for its use, but unknowingly secreted by the animal itself; formed, like Foraminifera shells, from lime drawn out of the water. Between these plates are tiny openings; and through those openings are put out the minute tube-feet. Even in armour made by skilled workmen for human beings, joints have always been necessary; and we know from history how many a gallant fighter in past centuries was slain by an arrow piercing where a joint allowed it to enter. Certain members of the immense Worm Family, living in the sea, wear protective scales and bristles; but these can only be named in passing. The great MOLLUSC Family is found throughout the whole Ocean, from sea to sea, from shore to shore, from the surface to the utmost depths. It includes numberless subdivisions, and enormous varieties in shape and size, in colouring and kind. It contains millions of the tiniest little fragile shells, such as those described by the poet in well-known lines:-- “Slight, to be crushed with a tap Of my finger-nail on the sand.” It contains also the giant clams of southern seas, the hugest bivalves ever seen, one pair of which may weigh five hundred pounds. A Mollusc is usually a soft-bodied creature, with a so-called “foot,” a nervous system, a mouth, a “mantle,” and a protecting one-valve or two-valve shell. The “mantle”--a peculiarity of this family--is a curious loose fold of the skin or wall of the body, wrapped round like a mantle. From the “mantle” is formed or secreted the hard shell, largely composed of carbonate-of-lime. In the shell itself there are no blood-vessels, there is no actual life; and it cannot grow, as the creature within it grows. Yet in a sense it grows, since by the addition of constant fresh layers to the edges it becomes larger and larger, thus accommodating itself to the increased size of its inhabitant. Mollusc shells are of all imaginable shapes and kinds; and often they are of extraordinary beauty.