From the broader portion of the planula an outgrowth arises which becomes the first tentacle of the cormus.
The athorome of Physophora, &c., consisting of siphon, tentacle, one or more palpons with palpacles, and one or more gonophores.
Tentacles are hollow; but in some cases the tentacle may become solid by obliteration of its cavity.
The base of a tentacle bisected in the middle line.
As a result of this extension of the umbrellar margin, all structures belonging to this region, namely, the ring-canal, the nerve-rings, and the rim of thickened ectoderm, do not run an even course, but are thrown into festoons, caught up under the insertion of each tentacle in such a way that the ring-canal and its accompaniments form in each notch of the umbrellar margin an inverted V, the apex of which corresponds to the insertion of the tentacle; in some cases the limbs of the V may run for some distance parallel to one another, and may be fused into one, giving a figure better compared to an inverted Y.