The little transparent embryos from which they arise, oval in form, with a slight, scarcely perceptible depression at one end, resemble the embryos of Coryne already described. They may be seen in great numbers in the spring, floating about in the water, or rather swimming,--for the motion of all Radiates in their earliest stage of existence is rapid and constant, in consequence of the vibratile cilia that cover the surface. At this stage of its existence such an embryo is perfectly free, but presently its wandering life comes to an end; it shows a disposition to become fixed, and proceeds to choose a suitable resting-place. I use the word "choose" advisedly; for though at this time the little embryo seems to have no developed organs, it yet exercises a certain discrimination in its selection of a home. Slightly pear-shaped in form, it settles down upon its narrower end; it wavers and sways to and fro, as if trying to get a firm foothold and force itself down upon the surface to which it adheres; but presently, as if dissatisfied with the spot it has chosen, it suddenly breaks loose and swims away to another locality, where the same examination is repeated, not more to its own satisfaction apparently, for the creature will renew the experiment half a dozen times, perhaps, before making a final selection and becoming permanently attached to the soil. In the course of this process the lower end becomes flattened, and moulds itself to the shape of the body on which it rests. Once settled, this animal, thus far hardly more than a transparent oblong body without any distinct organs, begins to develop rapidly. It elongates, forming a kind of cup-like base or stem, the upper end spreads somewhat, the depression at its centre deepens, a mouth is formed that gapes widely and opens into the digestive cavity, and the upper margin spreads out to form a number of tentacles, few at first, but growing more and more numerous till a wreath is completed all around it. In this condition the young Jelly-Fish has been described under the name of _Scyphostoma_. As soon as this wreath of tentacles is formed, a constriction takes place below it, thus separating the upper portion of the animal from the lower by a marked dividing-line. Presently a second constriction takes place below the first, then a third, till the entire length of the animal is divided across by a number of such transverse constrictions, the whole body growing, meanwhile, in height. But now an extraordinary change takes place in the portions thus divided off. Each one assumes a distinct organic structure, as if it had an individual life of its own. The margin becomes lobed in eight deep scallops, and a tube or canal runs through the centre of each such lobe to the centre of the body, where a digestive cavity is already formed. At this time the constrictions have deepened, so that the margins of all the successive divisions of the little Hydroid are very prominent, and the whole animal looks like a pile of saucers, or of disks with scalloped edges and the convex side turned downward. Its general aspect may be compared to a string of Lilac-blossoms, such as the children make for necklaces in the spring, in which the base of one blossom is inserted into the upper side of the one below it. In this condition our Jelly-Fish has been called _Strobila_.