To any one who hesitates to acknowledge that the sponge is endowed with animal life--confessedly in its lowest form, yet with a most exquisite adaptation to its destiny--we would offer the spectacle of a living sponge in a portion of its native element. We would let him gaze on the animated fountain, which is perpetually sucking the water into its substance through its countless pores, and after assimilating such particles of it as are essential to its existence, ceaselessly expelling it, at more distant intervals, through the larger channels which may be observed on its outer surface. We would point out innumerable gemmules of gelatinous matter, which at certain seasons of the year may be seen spouting "from all parts of the living film which invests the horny skeleton;"[24] until, at length, escaping from the nursery in which they grew, they are carried off to the wide sea by means of the force of the currents issuing from the sponge, though not left to perish at the mercy of the waves. For he will find that the young animal or egg is covered with numberless minute hairs or _cilia_, each one of which is endowed with a distinct and innate power of vibration; so that by means of thousands of almost invisible oars, the young sponge "shoots like a microscopic meteor through the sea," until it arrives at some rock or other place properly adapted for its future growth; then it settles calmly and contentedly down, and gradually losing its locomotive power, begins to spread on its base; and builds up, within its living substance, a horny framework, such as we have already seen in its parent. The above-named currents may be more distinctly seen by powdering the surface of the water with chalk or any similar substance; and Professor Grant mentions, that by placing pieces of cork or dry paper over the apertures, he could see them moving "by the force of the currents at the distance of ten feet from the table on which the specimen rested." Dr. Peysonell, who paid great attention to the structure of the sponge, brought proofs of its animal vitality before the Royal Society in the years 1752--57. And Mr. Ellis, five years afterward, by his dissections, set the question quite at rest; though he fell into the error of believing that the frame of the sponge was the outer case of worms or polypes. Later examination, however, has shown that the _frame_ or _sponge_, commonly so called, is an _internal_ skeleton, while the vital power is simply composed of a slimy film which coats over every fibre, and which, inert as it appears, possesses the power of secreting the particles essential to its growth. It has been affirmed, that the sponge is observed to contract or shrink when torn from the rooks; but there is satisfactory evidence to prove that neither this nor any degree of laceration has a sensible effect on this nerveless though vital mass.