The science of life : fully illustrated in tone and line and including many diagrams

LESS INDIVIDUALIZED ANIMALS

Fig. 102.

A group of Celenterates.

Below, from left to right, are four Plumose Anemones (Metridium), two of the green polyp-like jelly-fish Haliclystus, two Sea-

dahlias (Tealia) capturing prawns, and two kinds of coralline growth (Sertularia and Gorgonia), each the tubular dwelling

of acolony of tiny Polyps. Above, on the left, is a clear, milky-blue Jelly-fish (Aurelia), and, on the right, two glassy Sea-gooseberries (Pleurobrachia), of which one has just caught a young pipe-fish.

of crumpets sprouting tentacles, which detach themselves one by one and grow into jelly-fish.

The third class, the Actinozoa, includes the sea-anemones and corals. These animals exist only in the polyp phase, nomeduse being known, and their polyps are more highly and elaborately organized than those of any other group. Some, like the sea-anemones of our shores—the beadlet, the plumose anemone, the sea-dahlia and the restremain solitary through life, but in most cases, notably among corals, there is extensive budding, which results in the formation of more or less enormous colonies. The seaanemones, like Hydra, have a mouth surrounded by stinging tentacles ; in many species peculiar threads covered with particularly active stinging cells can be shot out through the mouth, or through special port-holes in the side of the body. The larger kinds—such as the dahlia anemonecan even capture prawns and small crabs.

The corals make a hard skeleton of lime, round which, and sometimes inside which, they live; they are nearly always colonial, and may build fan-like structures, rods like the pink “ dead man’s fingers ”’ of our coasts,

or massive reefs. The Great Barrier Reef of Australia, over a thousand miles long and fifty miles across, is the work of myriads of tiny coral-polyps. The Actinozoa are also remarkable for the brilliance and intensity of their coloration. Anybody who has prowled a rocky shore at low tide will know how varied the colours of sea-anemones can be. The tropical corals. are even more striking ; there are pink, yellow, green, and purple corals; corals with green polyps and crimson skeletons ; bright blue corals ; corals with scarlet, finger-like skeletons fringed with white polyps.

A fourth class, the Ctenophores, is sometimes classified with theccelenterates and sometimes put in a phylum by itself. The sea-gooseberry, Pleurobrachia, is a delicate transparent globe of jelly-like consistency that floats in the open sea. Running down the sides of its body there are eight comb-like structures, each tooth of the combs being a gigantic cilium ; the combs are in incessant motion, giving the animal a_ beautiful iridescent appearance, and thus it swims through the water. Trailing downwards (but capable of being drawn in) are two long tentacles set, not with stinging-capsules, but with

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