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_. [Illustration: Scyphostoma of Aurelia flavidula, our common white Jelly-Fish with a rosy cross.] [Illustration: Strobila of Aurelia flavidula.] While these organic changes take place in the lower disks, the topmost one, forming the summit of the pile and bearing the tentacles, undergoes no such modification, but presently the first constriction dividing it from the rest deepens to such a degree that it remains united to them by a mere thread only, and it soon breaks off and dies. This is the signal for the breaking up of the whole pile in the same way by the deepening of the constrictions; but, instead of dying, as they part, they begin a new existence as free Medusae. Only the lowest portion of the body remains, and around the margin of this tentacles have developed corresponding to those which crowned the first little embryo; this repeats the whole history again, growing up during the following season to divide itself into disks like its predecessor. [Illustration: Strobila of Aurelia flavidula: a, Scyphostoma reproduced at the base of a Strobila, bb, all the disks of which have dropped off but the last.]