On shells and stones, on sea-weeds or on floating logs, there may often be observed a growth of exquisitely delicate branches, looking at first sight more like a small bunch of moss than anything else. But gather such a mossy tuft and place it in a glass bowl filled with sea-water, and you will presently find that it is full of life and activity. Every branch of this miniature shrub terminates in a little club-shaped head, upon which are scattered a number of tentacles. They are in constant motion, extending and contracting their tentacles, some of the heads stretched upwards, others bent downwards, all seeming very busy and active. Each tentacle has a globular tip filled with a multitude of cells, the so-called lasso-cells, each one of which conceals a coiled-up thread. These organs serve to seize the prey, shooting out their long threads, thus entangling the victim in a net more delicate than the finest spider's web, and then carrying it to the mouth by the aid of the lower part of the tentacle. The complication of structure in these animals, a whole community of which, numbering from twenty to thirty individuals, is not more than an inch in height, is truly wonderful. In such a community the different animals are hardly larger than a good-sized pin's head; and yet every individual has a digestive cavity and a complete system of circulation. Its body consists of a cavity inclosed in a double wall, continuing along the whole length of each branch till it joins the common stem forming the base of the stock. In this cavity the food becomes softened and liquefied by the water that enters with it through the mouth, and is thus transformed into a circulating fluid which flows from each head to the very base of the community and back again. The inner surface of the digestive cavity is lined with brownish-red granules, which probably aid in the process of digestion; they frequently become loosened, fall into the circulating fluid, and may be seen borne along the stream as it passes up and down. The rosy tint of the little community is due to these reddish granules. [Illustration: Single head or branch of Coryne mirabilis magnified, with a Medusa bud: a, stem; c, club-shaped body; o, mouth; tt, tentacles; d, Medusa bud.]