BELOW the moss are four figures, which are, in fact, the same object differently magnified, and seen from different points of view. These peculiar organs are technically termed “cnidæ,” from a Greek word which signifies a nettle. The appropriateness of the name we shall presently see. I have already mentioned that the tentacles of various marine animals are furnished with poison-cells. The object of these cells is to capture and kill the prey, and the mode of doing so is very remarkable. On the right and left of the illustration are two such bodies, in which is seen a sort of elastic wire coiled spirally, apparently without regularity, but really possessing a most beautiful order. That on the left is the poison-cell of a Madrepore, and the other is the same organ in a Corynactis. No sooner is the tentacle touched than the poison-cells are mechanically acted upon. They are turned inside out, and the coiled spring darts forth with wonderful violence. Slight as is the dart, so fine that it cannot be seen except with the aid of a tolerably powerful microscope, it is a terrible weapon. Although it is projected with sufficient force to bury itself to its base even through so tough an object as the human skin, it could inflict but little injury, and would, indeed, scarcely be felt. But it carries with it a most irritant poison, which is apparently contained in the little capsule. These cnidæ are very plentiful in the tentacles of the Stinging Jelly-fish, or Stanger, as it is often called, and are charged with a terrible poison. As is the case with all such poisons, its effects differ according to the constitution of the being that is poisoned. There are some persons, for example, who care no more for the sting of a bee than for the prick of a needle, and there are those whom a single bee-sting will bring almost to the gates of death. So with the tentacles of the Stinging Jelly-fish and those of the Portuguese Man-of-war, and there are persons who are scarcely affected with the sting of the scorpion. So it is with nettles. When I was a boy at school it was thought necessary to wear an oak-leaf, or at least a portion of an oak-leaf, on the 29th of May, and all who did not possess this talisman might be flogged with nettles by those who did. As the school was situated in the north of England, where the oak puts forth its leaves late in the season, it was no easy matter to obtain a veritable oak-leaf, and we used to take any leaf that we could procure, and cut it round the edges into the similitude of a suitable oak-leaf. The effect of the nettles upon the boys was most curiously diversified. Some cared nothing whatever for them; others suffered sharp but brief pangs; while others, of whom I was one, endured the most lancinating pain at the time, and for hours afterwards a hot, burning, fevered skin, and a heavy, dull ache, accompanied by throbbings of the brain so violent that it appeared as if the head would burst asunder at every heart-beat.