[Illustration: 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 {318}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. [Illustration: 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.)] FAM. 1. CHARYBDEIDAE.—Cubomedusae with four interradial tentacles. {319}_Charybdea_ appears to have a very wide geographical distribution. Some of the species are usually found in deep water and come to the surface only occasionally, but others (_C. xaymacana_) are only found at the surface of shallow water near the shore. The genus can be easily recognised by the four-sided prismatic shape of the bell and the oral flattened expansion of the base of the tentacles. The bell varies from 2-6 cm. in length (or height) in _C. marsupialis_, but a giant form, _C. grandis_,[354] has recently been discovered off Paumotu Island which is as much as 23 cm. in height. The colour is usually yellow or brown, but _C. grandis_ is white and _C. xaymacana_ perfectly transparent.