or the sea-ball, in natural history, is the name of a substance very common on the shores of the Mediterranean, and elsewhere. It is generally found in the form of a ball about the size of the balls of horse-dung, and composed of a variety of fibrils irregularly complicated. Various conjectures have been given of its origin by different authors. John Bauhin tells us, that it consists of small hairy fibres and straws, such as are found about the sea plant called alga vitriariorum; but he does not ascertain what plant it owes its origin to. Imperatus imagined it consisted of the exuviae both of vegetable and animal bodies. Mercatus is doubtful whether it be a congeries of the fibrils of plants, wound up into a ball by the motion of the sea water, or whether it be not the workmanship of some sort of beetle living about the sea shore, and analogous to our common dung beetle's ball, which it elaborates from dung for the reception of its progeny. Schreberius says it is composed of the filaments of some plant of the reed kind; and Welckius supposes it is composed of the pappous part of the flowers of the reed. Maurice Hoffman thinks it the excrement of the hippopotamus; and others think it that of the phoca or sea calf. Klein, who had thoroughly and minutely examined the bodies themselves, and also what authors had conjectured concerning them, thinks that they are wholly owing to, and entirely composed of, the capillaments which the leaves, growing to the woody stalk of the alga vitriariorum, have when they wither and decay. These leaves, in their natural state, are as thick as a wheat straw, and they are placed so thick about the tops and extremities of the stalks, that they envelop, embrace, and lie over one another; and from the middle of these clusters of leaves, and indeed from the woody substance of the plant itself, there arise several other very long, flat, smooth, and brittle leaves. These are usually four from each tuft of the other leaves; and they have ever a common vagina, which is membranaceous and very thin. This is the style of the plant, and the pila marina appears to be a cluster of the fibres of the leaves of this plant, which cover the whole stalk, divided into their constituent fibres; and by the motion of the waves first broken and worn into short shreds, and afterwards wound up together into a roundish or longish ball.

Pila, was a ball made in a different manner according to the different games in which it was to be used. Playing at ball was very common amongst the Romans of the first distinction, and was looked upon as a manly exercise, which contributed both to amusement and health. The pila was of four sorts: 1st, Follis or balloon; 2nd, Pila Trigonalis; 3rd, Pila Paganica; 4th, Harpastum. All these come under the general name of pila. For the manner of playing with each of them, see the articles FOLLIS, TRIGONALIS, PILASTER, in architecture. See there, no 50, &c.