UNTIL the late Prof. Agassiz in 1859 announced his discovery that the Milleporidae were Hydroids and not Anthozoans, it was confidently believed that all living recent stony corals were most closely allied in their essential structure to the common sea anemones of our coasts. The majority of stony corals still remain under the old category. The beautiful calcareous branched or variously formed objects so familiar as ornaments or as exhibits in museums are nearly all of them formed within the bodies of animals which differ in no important features from the flower-like anemones of our aquariums. The sea anemones have no hard skeleton to support their soft and yielding bodies; the corals differ from them in that they have such skeletons. These are, during the life of the animals of which they form part, entirely embedded within the soft tissues, and only become exposed and appear in the familiar form when the animals are dead and their flesh has been removed from their bones by the action of decomposition or more speedy solution by means of caustic alkalis.