In Cephalodiscus the coenoecium is more massive, and may contain a continuous irregular cavity in which the zooids live (Demiothecia), or may be secreted in such a way that each zooid has its own independent tube (Idiothecia, Orthoecus).
The zooids are a modification of the type of structure known in Balanhglossus, from which they differ principally in the following respects: (i.) The alimentary canal, instead of being straight, has a U-shaped flexure, the dorsal line between the mouth and the anus being short.
The original specimen of C. dodecalophus contained exclusively female zooids, in which a single pair of ovaries (figs.
Associated with these males are neuter zooids, which usually possess no functional repro ductive organs, but have in I -...
Hence it is necessary to distin guishbetween,first,the"zooids," FIG.
- Dasychone zooids are formed from a zone of budding 4.
Ultimately, a chain of sexual Malmgren.) zooids is thus formed.
A given stock only produces zooids of one sex.
Zooids possessing a high degree of individuality.
Zooids usually connected laterally with their neighbours.
Body-cavities of zooids not continuous with one another.
Body-cavities of zooids continuous with one another.
- Part of the creeping stolon, with zooids, of Pedicellina belgica.
A, c, Stalks of zooids of different ages; b, bud.
Ctenostomata the colony is similarly constituted, a branched stolon giving off the zooids, which are not connected with one another.
In the majority of Ectoprocta there is no stolon, the zooids growing out of one another and being usually apposed so as to form continuous sheets or branches.
In the encrusting type, which is found in a large proportion of the genera, the zooids are usually in a single layer, with their orifices facing away from the substratum; but in certain species the colony becomes multilaminar by the continued superposition of new zooids over the free surfaces of the older ones, whose orifices they naturally occlude.
The zoarium may rise up into erect growths composed of a single layer of zooids, the orifices of which are all on one surface, or of two layers of zooids placed back to back, with the orifices on both sides of the fronds or plates.
The zooids of which the colonies of Ectoprocta are composed consist of two parts: the body-wall and the visceral mass (figs.