"To-day I saw the Dragon-fly Come from the wells where he did lie; An inner impulse rent the veil By his old husk: from head to tail Came out clear plates of sapphire mail. He dried his wings: like gauze they grew, Through croft and pasture wet with dew, A living flash of light he flew." --TENNYSON. If in your walks abroad you should meet with a pool of turbid water, do not object to linger for a moment on its brink. Nature, as a reward for your trouble, will gratify you with an extraordinary surprise. Stir up the mud with a stick, or, better still, with your hand; and then, as the children say, you shall see--what you shall see! Oh, what an ugly creature is struggling in this handful of slime! It looks like a large spider! Nay, examine it more attentively; it can do you no harm. Well, it is a singular animal; greenish in colour, bristling with hairs, and covered with mud. It is not a spider, for it has only six legs and these are exactly like the legs of insects. I can distinctly make out three joints (articulations) to each tarsus, which terminates in a simple hook. The belly is formed of regular segments; is rounded above, and flat underneath. What do I see? On the top, and nearly in the middle, each ring is armed with a spine, so that the row of spiny projections remind one of the back of a crocodile. Pray tell me, what is this curious creature? Before I tell you, I would have you more thoroughly acquainted with it. Continue your examination. The face has a strange expression; it looks--the insect, I mean--like a masked knight. Its mask, formed of a scaly substance and thoroughly compact, is composed of two pieces, which are separated from one another by a transversal suture: the upper, which is broader than it is high, we may call the vizor; it consists of two lobes, soldered together longitudinally; the lower, which is higher than it is broad, will be the chin-piece; it is triangular in shape, and its base rests against the vizor, while the summit is jointed or articulated with a support, which acts as a hinge when the mask is raised or lowered. These movements, let me tell you, are voluntary; the animal raises its mask to arrest on their way the Infusoria and other animalcules on which it feeds. For crushing them, it is provided with strong mandibles, which you can detect by lowering the mask with a pin, or the point of a penknife. The eyes, which resemble little mammillary protuberances, are situated above and outside of the vizor. On the animal's back, where the belly joins the thorax, do you observe those four little sheath-like or scabbard-like tongues? The extremity of the body, the tail, is marked by three conspicuous triangular points, lying close to the opening, through which the water enters and issues, as if it were alternately sucked in and poured out by a piston. This, you must understand, is the respiratory apparatus. (See Fig. 40.)