The visceral mass was accordingly termed the "polypide" and the body-wall which contains it the "zooecium."
This view depended principally on the fact that the life of the polypide and of the zooecium are not coextensive.
On the degeneration of the polypide, its nutritive material is apparently absorbed for the benefit of the zooid, while the pig mented substances assume a spheroidal form, which either remains as an inert "brown body" in the body-cavity or is discharged to the exterior by the alimentary canal of the new polypide.
This is formed as a two-layered "polypide-bud," which usually develops from the inner side of the zooecial wall, and soon occupies the place of the previous polypide.
The polypide consists of a "lophophore" bearing a series of ciliated tentacles by which Diatoms and other microscopic bodies are collected as food, of a U-shaped alimentary canal, and of a central nervous system.