Millepore (Millepora Linn), a genus of hydroid medusae The animals live in communities, which take on various arborescent and incrusting shapes; they deposit much carbonate of lime in their tissues, so that the medusa stock is in outward appearance almost solid, with minute pores on the surface which contain the animals. A cross section of this stony skeleton shows that the minute individuals of the community constantly grow outward in the direction of their longitudinal axis, forming as they proceed long calcareous tubes, which are so intimately cemented together as to make a compact mass. Across these tubes, at short intervals, are formed little transverse platforms, which divide the tubes into joints or cells. These platforms are deposited by the base of the animal, and are of high importance in classification; by them is characterized Milne-Edwards's division of the tabulata, which includes millepora. Till within a short time all zoologists have placed the millepores among polyps. In the winter of 1857-'8 Prof. Agassiz succeeded, for the first time, in observing the animals of millepora alcicornis in Florida, and was surprised to find them not polyps, but true hydroid medusae, resembling hydractiniae.

This observation gives great importance to the medusae, as represented among the fossils, for the tabulata are found abundantly as low as the Silurian formations. As the presence of mesenteric septa seems to militate against the above mentioned separation, some naturalists retain them among the polyps. - See "The British Fossil Corals," by Milne-Edwards, in the "Transactions of the Palaeontographical Society;" Dana's "Zoophytes" and "Corals and Coral Islands;" the "American Journal of Science," vol. xxvi., p. 140 (1858); and Agas-siz's " Contributions to the Natural History of the United States," vol. iii.

Millepora alcicornis.

Millepora alcicornis.