The class Hydrozoa includes seven orders, first and principally of which let us speak of the Medusæ, of which the ordinary “jelly‐fish” is a familiar example. This great order (_Medusidæ_) is characterised by having a disc, more or less convex above, resembling a mushroom or expanded umbrella, the edges of the umbrella, as well as the mouth and suckers, commonly having tentacula, or feelers, and cilia. Taken from the sea, a Medusa weighing fifty ounces will rapidly dissolve away to a few grains of solid matter. These floating umbrellas or mushrooms, as they might be termed, are of many forms, but they are all to be counted among the most beautiful works of the Creator. Sometimes the animal is transparent as crystal, sometimes opaline, now of a delicate rose or azure‐blue colour, now yellow, now violet, and now, again, reflecting the prismatic colours. “The Medusæ are animals without much consistence, containing much water, so that we can scarcely comprehend how they resist the agitation of the waves and the force of the currents; the waves, however, float without hurting them, the tempest scatters without killing them. When the sea retires, or they are withdrawn from their native waters, their substance dissolves, the animal is decomposed, they are reduced to nothing; if the sun is strong this disorganisation occurs in the twinkling of an eye, so to speak.” If they are touched ever so lightly while swimming, they contract their tentacula, fold up their umbrella, and sink into the depths of the sea. At one period of the year the Medusæ are charged with numbers of minute eggs, which are suspended in festoons—crystalline roes they might be termed—from their bodies, and which in due time become living organisms.