- Surface view of the Subumbrella or oral aspect of Aurelia aurita, to show the position of the openings of the subgenital pits, GP. In the centre is the mouth, with four perradial arms corresponding to its angles (compare fig.
X indicates the outline of the roof (aboral limit) of a subgenital pit; y, the outline of its floor or oral limit, in which is the opening.
Usually the four subgenital cavities are distinct from each other (so-called tetrademnic condition), but in many Rhizostomeae, for example, Crambessa, the subgenital cavities join together under the subumbral floor of the stomach (so-called monodemnic condition) and coalesce to form a so-called subgenital portico placed on the oral side of the stomach, opening by four interradial apertures between the oral arms, that is to say, by the four primitive apertures of the subgenital pits.
In Nausithoe subgenital pits are absent altogether, and the same condition may be found in Charybdaeidae.
(After Claus.) by Friedemann (3), a recent investigator of the subject, that the infundibular cavities appear late in the scyphistoma and have no relation either to the septal muscles or to the subgenital cavities of the adult.