The Scyphistoma may remain as such for some time, during which it reproduces by budding, and in some localities it may be found in great numbers on seaweeds and stones.[[352]]
In the course of time, however, the Scyphistoma exhibits a ring-like constriction of the body just below the crown of tentacles, and as this deepens the general features of a Scyphomedusa are developed in the free part above the constriction. In time this free part escapes as a small free-swimming jelly-fish, called an "Ephyra," while the attached part remains to repeat the process. In many species the first constriction is followed by a second immediately below it, then a third, a fourth, and so on, until the Scyphistoma is transformed into a long series of narrow discs, each one acquiring, as it grows, the Ephyra characters. Such a stage has been compared in form to a pile of saucers, and is known as the "Strobila."
The Ephyra differs from the adult in many respects. The disc is thin and flat, the manubrium short, the margin of the umbrella deeply grooved, while the statorhabs are mounted on bifid lobes which project outwards from the margin. The stabilisation of the Scyphistoma is a process of reproduction by transverse fission, and in some cases this is supplemented by gemmation, the Scyphistoma giving rise to a number of buds which become detached from the parent and subsequently undergo the process of strobilisation.
Fig. 144.—The perisarc tubes of a specimen of Spongicola fistularis (N) ramifying in the skeleton of the Sponge Esperella bauriana (Sp.), as seen in a macerated specimen, × 1. (After Schulze.)
The Scyphistoma of Nausithoe presents us with the most remarkable example of this mode of reproduction (Fig. 144), as it forms an elaborate branching colony in the substance of certain species of sponges. The ectoderm secretes a chitinous perisarc, similar to that of the hydrosome stage of many of the Hydrozoa, and consequently Stephanoscyphus (Spongicola), as this Scyphistoma was called, was formerly placed among the Gymnoblastea. It is remarkable that, although the Scyphozoan characters of Spongicola were proved by Schulze[[353]] in 1877, a similar Scyphistoma stage has not been discovered in any other genus.
Order I. Cubomedusae.
Scyphozoa provided with four perradial statorhabs, each of which bears a statolith and one or several eyes. There are four interradial tentacles or groups of tentacles. The stomach is a large cavity bearing four tufts of phacellae (Fig. 145, Ph), situated interradially. There are four flattened perradial gastric pouches in the wall of the umbrella which communicate with the stomach by the gastric ostia (Go). These pouches are separated from one another by four interradial septa; and the long leaf-like gonads are attached by one edge to each side of the septa. In many respects the Cubomedusae appear to be of simple structure, but the remarkable differentiation of the eyes and the occurrence of a velum (p. [313]) suggest that the order is a highly specialised offshoot from a primitive stock.
Fig. 145.—Vertical section in the interradial plane of Tripedalia cystophora. Go, Gastric ostia; Man, manubrium; Ph, group of phacellae; T, tentacles in four groups of three; tent, perradial sense-organs; V, velum. (After Conant.)