its Worm-like stage within the egg as much as the Butterfly that we knew a few months ago as a Caterpillar. In the same way certain of the higher Radiates undergo all their transformations, from the Polyp phase of growth to that of Acaleph or Echinoderm, after birth; while others pass rapidly through the lower phases of their existence within the egg, and are born in their final condition, when all their intermediate changes have been completed. We have appropriate names for all the aspects of life in the Insect: we call it Larva in its first or Worm-like period, Chrysalis in its second or Crustacean-like phase of life, and Imago in its third and last condition as Winged Insect. But the metamorphoses of the Radiates are too little known to be characterized by popular names; and when they were first traced, the relation between their different phases of existence was not understood, so that the same animal in different stages of growth has frequently been described as two or more distinct animals. This has led to a confusion in our nomenclature much to be regretted; for, however inappropriate it may be, a name once accepted and passed into general use is not easily changed. That early stage of growth, common to all Radiates, in which they resemble the Polyps, has been called the Hydra state, in consequence of their resemblance to the fresh-water Hydra to be found in quantities on the under side of Duck-Weed and Lily-pads. For any one that cares to examine these animals, it may be well to mention that they are easily found and thrive well in confinement. Dip a pitcher into any pool of fresh water where Duck-Weed or Lilies are growing in the summer, and you are sure to bring up hundreds of these fresh-water Hydrae, swarming in myriads in all our ponds. In a glass bowl their motions are easily watched; and a great deal may be learned of their habits and mode of life, with little trouble. Such an animal soon completes its growth: for the stage which I have spoken of as transient for the higher Radiates is permanent for these; and when the little sphere moving about by means of its vibratile cilia has elongated a little, attached itself by the lower end to some surface, while the inversion of the upper end has formed the mouth and digestive cavity, and the expansion of its margin has made the tentacles, the very simple story of the fresh-water Hydra is told. But the last page in the development of these lower Radiates is but the opening chapter in that of the higher ones, and I will give some account of their transformations as they have been observed in the Acalephs. [Illustration: Coryne mirabilis, natural size]