The sponges in their habits show a variety of tastes. Many grow in the mud, the majority upon rocks. On the New England shores there is one of a yellowish hue which lives in the sand. It is very light, and the pores are so fine that the sand does not enter them. After a storm on Cape Cod thousands are found on the beaches, blown far inshore. Black and pure white sponges are found in fresh water as well as in salt. They increase by depositing eggs. In one stage of their development the young (Fig. 14, V.) are free-swimming animals.
III. THE JELLYFISHES
Fig. 19.—A jellyfish (Pelagia).
Among the most beautiful and fragile of all animals are the singular forms which we call jellyfishes (Fig. 19). They are so delicate that we can not lift them, and in many instances they have ninety-five per cent of water in their composition. They would almost seem to be purely ornamental did we not know that they fill an important niche in the hall of nature, constituting almost the sole food of many whales.
The jellyfishes are found in all waters, salt and even fresh. They may be seen floating near or at the surface, often in vast numbers. Sometimes they are found deep in the heart of the upper part of the ocean, often in such quantities that the water appears to be filled with their graceful shapes.
In the Santa Catalina Channel a beautiful lavender-hued form is common, the water being alive with them at times, and I have seen specimens with tentacles streaming behind them an estimated length of twenty feet, the entire animal appearing like a huge comet in the blue sky of the ocean. Mrs. Agassiz describes a jellyfish called Cyanea which was six feet across its disk and which had tentacles over one hundred feet in length. Specimens have been seen in East Indian waters which were much larger, having an estimated weight of several tons. An English naturalist describes one which stranded in India and gave out so vivid a light at night that the natives were afraid to approach it; yet large as was this monster, a few hours in the sun caused it to disappear or literally evaporate, water forming so large a part of its make-up.
In appearance the jellies resemble umbrellas, dinner plates, or inverted bowls, from which depend streamers or tentacles of various kinds and shapes, often richly colored, especially the very minute forms. The mouth is in the center, the eyes are around the edge of the disk, while the huge tentacles, which can be lifted or lowered as fancy dictates, are so many fishing lines by which this jelly finds its food. I have often watched them floating near the surface, the delicate vermilion-tinted tentacles floating gracefully about, and serving as so many tempting baits. Should a sardine or other small fish venture to attack this tempting lure, we can almost imagine it struck by an electric shock, as it rolls over dead. The secret is very easily discovered. Lift the tentacles with the hand and a burning sensation will be experienced, in some cases very painful. The tentacles of the jellyfish are armed with stings.