Jellyfishes are among the very oddest creatures which are found in the sea; for their bodies are made up almost entirely of sea-water! It is quite true, of course, that if you cut them in two the water does not run away. But then if you cut a cucumber in two the water does not run away; and yet cucumbers are made almost entirely of water. And the reason why it does not run away is just the same in each case. Both in the cucumber and in the jellyfish the water is contained in a very large number of very tiny cells; and if you cut either of them across you only divide a very small number of the cells, so that only a very small quantity of water escapes. But if you leave a jellyfish lying on the beach in the hot sunshine, and come back to look for it two or three hours later, you will not find it. All that you will find will be a ring-shaped mark in the sand, showing where the jellyfish had been lying, with just a few threads of animal matter in the middle. All the rest will have evaporated, because it was nothing else but water. All the same, jellyfishes are very wonderfully made; and perhaps the most wonderful thing of all about them is the fringe of long, slender threads which hangs down from the edges of their bodies. For these are the fishing-lines by means of which they catch their prey. Jellyfishes feed on all sorts of tiny creatures--the fry of fishes, and the zoeas of shrimps and prawns, for instance--and if you were to see one of these swim up against those terrible threads, you would notice that it at once became paralysed, and that in a very few moments it would be dead. The fact is that all the way along these threads are set with hundreds and hundreds of tiny oval cells, each of which has a very slender dart, with a barbed tip, coiled up like a watch-spring inside it. And the cells are made in such a way that as soon as they are touched they fly open, and the little darts leap out. So, you see, if any small creature swims up against the threads numbers of darts at once bury themselves in its body. And, as these darts are poisoned, it dies in a very short time. Jellyfishes can swim through the water by spreading and contracting their umbrella-shaped bodies, and you may sometimes see them travelling about in such enormous numbers that the water is perfectly thick with them. PLATE XL THE STINGING JELLYFISH (1) Sometimes, after a strong south-westerly wind has been blowing for a day or two in the early part of the autumn, you may find a brownish yellow jellyfish lying upon the shore. It has a circular body about as big as a soup-plate, fringed all the way round with great masses of long yellow hairs. And if you find one of these creatures you are almost sure to find another before very long, and then another, and then another; for they nearly always swim about in shoals together.