The gonophores of the Stylasterina are situated in large oval or spherical cavities called the ampullae, and their presence can generally be detected by the dome-shaped projections they form on the surface of the coral. The female gonophore consists of a saucer-shaped pad of folded endoderm called the "trophodisc," which serves the purpose of nourishing the single large yolk-laden egg it bears; and a thin enveloping membrane composed of at least two layers of cells. The egg is fertilised while it is still within the ampulla, and does not escape to the exterior until it has reached the stage of a solid ciliated larva. All the Stylasterina are therefore viviparous. The male gonophore has a very much smaller trophodisc, which is sometimes (_Allopora_) prolonged into a columnar process or spadix, penetrating the {285}greater part of the gonad. The spermatozoa escape through a peculiar spout-like duct which perforates the superficial wall of the ampulla. In some genera (_Distichopora_) there are several male gonophores in each ampulla. The gonophores of the Stylasterina have been regarded as much altered medusiform gonophores, and this view may possibly prove to be correct. At present, however, the evidence of their derivation from Medusae is not conclusive, and it is possible that they may have had a totally independent origin. _Distichopora_ and some species of _Stylaster_ are found in shallow water in the tropics, but most of the genera are confined to deep or very deep water, and have a wide geographical distribution. No species have been found hitherto within the British area. [Illustration: FIG. 136.—A portion of a branch of _Cryptohelia ramosa_, showing the lids _l_ 1 and _l_ 2 covering the cyclosystems, the swellings produced by the ampullae in the lids _amp_^1, _amp_^2, and the dactylozooids, _dac._ × 22. (After Hickson and England.)] A few specimens of a species of _Stylaster_ have been found in Tertiary deposits and in some raised beaches of more recent origin, but the order is not represented in the older strata. FAM. STYLASTERIDAE.—All the genera at present known are included in this family. _Sporadopora_ is the only genus that presents a superficial general resemblance to _Millepora_. It forms massive, branching white coralla, with the pores scattered irregularly on the surface, and, like many varieties of _Millepora_, not arranged in cyclosystems. It may, however, be distinguished at once by the presence of a long, brush-like style in each of the gastropores. The ampullae are large, but are usually so deep-seated in the coenenchym that their presence cannot be detected from the surface. It was found off the Rio de la Plata in 600 fathoms of water by the "Challenger."