The section Fungacea presents us with some exceptional and remarkable forms of asexual reproduction. The embryo _Fungia_ gives rise to a conical fixed coral called a "trophozooid." The upper part of the calyx of this trophozooid expands and becomes disc-shaped. This is called the "anthocyathus," and after it has reached a certain size it breaks away from the rest of the trophozooid as an adult _Fungia_. Several anthocyathi may be formed in succession from one trophozooid. This may be described as a process of successive transverse fission. In _Diaseris_ the disc divides into four quadrants, and each quadrant appears to be capable of acquiring the shape and size of the undivided parent. {389}Without doubt a process of sexual reproduction occurs in all Madreporaria. In some genera sexual reproduction appears to be almost continuous throughout the year; in others the sexual organs are formed only at periods separated by considerable intervals of sterility. According to the researches of Duerden the Madreporaria appear to be usually viviparous, the early stages of development are passed through within the body of the parent, and the young coral is discharged into the water as a free-swimming ciliated larva. The larvae are spheroidal, oval, or pear-shaped, but change their shape a good deal, and sometimes become elongated, straight, or spirally twisted rods. The larvae are at first dense and opaque, but subsequently they become distended by the absorption of water, and more nearly transparent. They swim about for one or two days, and then settle down by the aboral pole and become fixed. The tentacles are not formed, in any species that has yet been observed, during the free-swimming stage of existence. [Illustration: FIG. 171.—A fixed stage in the development of _Fungia_. The trophozooid has become differentiated into a discoid crown, the anthocyathus (_Cy_) and a pedicle, the anthocaulus (_Ca_). (After G. C. Bourne.)] DISTRIBUTION OF REEF CORALS.—The principal reef-forming corals reach their greatest size and grow with greatest rapidity in the warm, shallow waters of the world, but they are not confined to this habitat. A species of _Madrepora_ has been found in the very cold waters of Archangel, and _Manicina areolata_ occurs in Simon's Bay, Cape of Good Hope, many degrees south of the region of the East African coral reefs. As regards the distribution of these corals in depth, very little is known at present. The face of the growing coral reef that is turned towards the open sea is so steep that it has been found impossible to determine to what depth the living reef corals actually extend.