To have a regular ascent, we must commence from a very low stage, from the elementary embryon, which at the outset will have no other movement than that of the elements. The new creature is the mere serf of the planet; so completely so, that even in the egg, it turns as the earth turns, with its double turning on its own axis, and the general rotation. Even when emancipated from the egg, growing up, become adult, it will still remain the embryon, the soft mollusc. It will vaguely represent the progress of the superior lives; it will be as the foetus, as the larvæ or nymph of the insect, in which, folded and hidden, there yet are the organs of the winged creature which is yet to come. One trembles for a creature so weak; even the polypus though not less soft is less in danger. Having life equally in all its parts, wounds, even mutilations will not kill the polypus: wounded and mutilated he still lives on, apparently forgetful of the excised parts. But the centralised mollusc is far more vulnerable. What a door in his ease is open to death! The uncertain motion of the Medusa, which sometimes, perchance, may save her; the mollusc, at least at the outset, possesses but very slightly. All that is granted to him is his sloughing or exuding a gelatine matter, which walls him in, and replaces the cuirass of the oursin and the oursin's rock. The mollusc has the advantage of finding his defence within himself. Two valves form a house, light and fragile, indeed, so much so that those which float are transparent; in the case of those which are to be stationary, the mucus forms a filamentary anchoring cable, called the hyssas. It is formed exactly as silk is from an element originally quite gelatinous. The gigantic Iridacne, moors so fast by that cable, that the Madrepores mistake it for an islet, build upon it, envelope it, and strangle it. Passive and motionless life. It has no other event than the periodical visit of the sun and light, and no other action but to absorb what comes, and to secrete the jelly which makes the house, and will by degrees do the rest. The attraction of the light, always in the same direction, centralizes the view; and behold the eye. The secretion fixed by a constant effort, becomes an appendage, an organ which lately was a cable, and which by and bye will become the foot, a shapeless and inarticulated mass, which will bend itself to anything. It is the fin of those that swim, the pick of those that burrow in the sand, and the foot of those who at first rather crawl than walk. Some species arch it so that they can make a clumsy essay at leaping.