Some of these jelly-fish, or Medusæ, as they are called, are pounds in weight; but after a while only a shred of membrane-looking stuff remains, the water which makes up nearly all the animal having drained away. It is evident that the large Medusæ grow from small ones, and that there are many kinds of them, some of which are always small. A great jelly-fish, two feet across, was once a little one, leading exactly the same life. They grow, and to grow they must have nourishment; they are never still, and their muscles, transparent as they may be, have to be nourished, or their strength would soon give way. They require not only food, but also air in the water, so that they consume it, and make its oxygen gas of use to them. They seek the light in a remarkable manner, and get out of the way of things very gracefully, and their motions are rhythmical, like the ticks of a clock, in succession. Have they nerves and eyes? Science answers in the affirmative. These creatures, consisting of a vast proportion of sea-water, breathe, digest, and feed. More than this, they produce young; and if they are pale in color, bluish, or roseate in hue during the day, they are the glory of the deep during the night; and each one is a globe of light, the luminousness being the result of the action of the mysterious energy of life upon matter. Many of the jelly-fish found on the shores dead and injured are eighteen inches across, and it is not uncommon to see one swimming freely whose body is larger than that. Yet in spite of this size, and of the gifts of the creature, it has one of the shortest of lives, and it is born, grown, and dead between the spring and the winter. [Illustration: Typical Radiolaria 1, Rhizosphæra; 2, Sphærozoum; 3, Actinomma; 4, Lithomespilus; 5, Ommatocampe; 6, Carpocaium; 7, Challengeron; 8, Heliosphæra; 9, Clathrocyclas; 10, Dictyophimus]