There are a great many different forms of them, but they mostly agree in having their bodies shaped something like an umbrella, with long filaments hanging down from them. This is a picture of one of the kind called Berenice. It takes its name from the resemblance of its filaments, to the long hair of a lady. Berenice was the wife of a warrior, who made a vow to sacrifice the hair of her head, which was singularly beautiful, to Venus, if her husband returned from some successful exploit in which he was engaged. He did so, and the lady accordingly hung up her hair in the temple of Venus, and thereby gained the honor of giving her name to a constellation called the hair of Berenice, and the curious animal figured in the cut. The substance of the body is a mere mass of jelly, mostly quite transparent, but sometimes tinged with blue or green; and when deprived of life it becomes merely a salt liquid, and an extremely thin skin, weighing only a few grains. The mouth is underneath, in amongst the filaments, which seem to be placed where they are for the purpose of entangling small fish and insects, to hold them till the Acalepha can swallow them. A very great number of them are of a kind called Medusa, from the resemblance of their filaments to the snakes, which were said to take the place of hair upon the head of Medusa, one of the Furies. One or two sorts have a crest which they erect as a sail, and thus move along before the wind, on the surface of the sea, in calm weather. I will show you the picture of one of these called the Physalia. [Illustration] The size varies from that of a pin's head, to a foot or more in diameter, and it is said that some have been found to weigh as much as 50 pounds. Their weight is a very little more in proportion to their bulk than that of salt water, and they keep themselves afloat on the surface, as long as they are inclined, by moving very slowly along, which they do by alternately contracting and expanding a very light ring of muscle, which surrounds the umbrella. When they are tired of their snail's gallop, or they want to descend on any other account, they cease moving, and down they go. In this respect they are just like a man swimming, who sinks if he ceases to strike with his limbs.