Cavity of the zooecium subdivided by transverse diaphragms, most numerous in the distal portion.
This view depended principally on the fact that the life of the polypide and of the zooecium are not coextensive.
It is one of the most remarkable facts in the natural history of the Polyzoa that a single zooecium may be tenanted by several polypides, which successively degenerate.
In a few Gymnolaemata the ectocyst is merely chitinous, although in most cases the four vertical walls and the basal wall of the zooecium are calcareous.
8 A, 9 A), but in many Cheilostomes the frontal surface is protected by a calcareous shield, which grows from near the free edges of the vertical walls and commonly increases in thickness as the zooecium grows older by the activity of the "epitheca," a layer of living tissue outside it.