6. _Gonostyles_, appendages which produce by budding medusae or gonophores, like the blastostyles of a hydroid colony. In their most primitive form they are seen in _Velella_ as "gonosiphons," which possess mouths like the ordinary sterile siphons and bud free medusae. In other forms they have no mouths. They may be branched, so-called "gonodendra," and amongst them may occur special forms of palpons, "gonopalpons." The gonostyles have been compared to the blastostyles of a hydroid colony, or to the manubrium of a medusa which produces free or sessile medusa-buds. 7. _Gonophores_, produced either on the gonostyles already mentioned or budded, as in hydrocorallines, from the coenosarc, i.e. the stem (fig. 68, i.). They show every transition between free medusae and sporosacs, as already described, for hydroid colonies. Thus in _Velella_ free medusae are produced, which have been described as an independent genus of medusae, _Chrysomitra_. In other types the medusae may be set free in a mature condition as the so-called "genital swimming bells," comparable to the _Globiceps of Pennaria_. The most usual condition, however, is that in which sessile medusoid gonophores or sporosacs are produced. The various types of appendages described in the foregoing may be arranged in groups termed _cormidia_. In forms with a compact coenosarc such as _Velella_, _Physalia_, &c., the separate cormidia cannot be sharply distinguished, and such a condition is described technically as one with "scattered" cormidia. In forms in which, on the other hand, the coenosarc forms an elongated, tubular axis or stem, the appendages are arranged as regularly recurrent cormidia along it, and the cormidia are then said to be "ordinate." In such cases the oldest cormidia, that is to say, those furthest from the nectosome, may become detached (like the segments or proglottides of a tape-worm) and swim off, each such detached cormidium then becoming a small free cormus which, in many cases, has been given an independent generic name. A cormidium may contain a single nutritive siphon ("monogastric") or several siphons ("polygastric"): [Illustration: From G. H. Fowler, after G. Cuvier, Lankester's _Treatise on Zoology_. FIG. 71.--Upper surface of _Velella_, showing pneumatophore and sail.] The following are some of the forms of cormidia that occur:-- 1. The _eudoxome_ (Calycophorida), consisting of a bract, siphon, tentacle and gonophore; when free it is known as _Eudoxia_. 2. The _ersaeome_ (Calycophorida), made up of the same appendages as the preceding type but with the addition of a nectocalyx; when free termed _Ersaea_. 3. The _rhodalome_ of some _Rhodalidae_, consisting of siphon, tentacle and one or more gonophores. 4. The _athorome_ of _Physophora_, &c., consisting of siphon, tentacle, one or more palpons with palpacles, and one or more gonophores.