A median mesentery running dorsoventrally supports the alimentary canal and is continued behind it into the tail, thus dividing the body cavity into two lateral halves.
In some genera, for instance, Cyanea and its allies the gonad as a whole protrudes through the subgenital cavity as if it had undergone a hernia, and hangs down in the subumbral space as if suspended by a mesentery (fig.
Each mesentery is attached by its upper margin to the peristome, by its outer margin to the body-wall, and by its lower margin to the basal disk.
The postseptal coelom is partially divided by a ventral mesentery which is attached along the entire length of the convex.
The collarcavity (b.c. 2) is paired, although its ventral mesentery is not complete.
Each mesentery has a filament; but two of them, namely, the pair farthest from the sulcus, are longer than the rest, and have a different form of filament.