According to the observations of Mr. Carter, sponges begin their lives as solitary Amœbæ which grow by multiplication into masses, and assume endless forms according to the species; turbinate, bell-shaped, like a vase, a crater, a fan, flat, foliaceous and lobed or branching and incrusting the surface of stones. All the Amœbæ are so connected as to form one compound animal. The whole substance of a sponge is permeated by innumerable tubes which begin in small pores on the surface, and continually unite with one another as they proceed in their devious course to form a system of canals increasing in diameter and ending in wide openings called oscula, on the opposite side of the mass. Currents of water enter through the pores on the surface, and bring minute portions of food which are seized upon by a vast multitude of Amœbæ with long cilia which form the walls of the tubes and canals; and after they have extracted the nutritious part, the offal is carried into the sea through the oscula, by the current of water whose flux is maintained by the vibrations of the cilia. In the compressed and many of the tubular sponges the water passes through them in a straight line; in branched and encrusting sponges, the afferent and efferent openings are on the same surface. The water is inhaled continuously and gently like an animal breathing, but it is rapidly and forcibly ejected; and in its passage it no doubt furnishes oxygen to aërate the juices of the compound animal, whose flesh or sarcode is irritable while alive, and which has the power to open and shut the pores and oscula of the canals, for the whole sponge forms one compound creature whose mass is nourished by the myriads of Amœbæ of which it is constituted. Within the animated sarcode mass of the sponges there is in most cases a complicated skeleton of fibrous network, either horny, calcareous, or siliceous, which supports the soft mass, and determines its form. Besides the skeleton, the mass of sponges is for the most part strengthened and defended by siliceous, and more rarely by calcareous, spines or spicules, either imbedded among the fibres of the skeleton, or fixed to them by their bases. The fibres of the skeleton network always unite, whether they be horny, calcareous, or siliceous; the spicules never, though they often lie in confused heaps over one another. They are of innumerable forms and arrangements. Some are like long needles lying close together in bundles, pointed or with a head like a pin at one or both ends; a great number are stellate with long or short rays; there may even be several different forms in the same sponge. Many calcareous sponges have cavities full of organic matter; and when the calcareous matter is dissolved by dilute acid, the organic base is left.