- All known hydropolyps possess the power of reproduction by budding, and the buds produced may become either polyps or medusae.
From the stolon the daughter-polyps grow up vertically.
After a time the polyps, or certain of them, produce by budding medusa-individuals, which sooner or later develop sexual elements; in some cases, however, the founder_ polyp remains solitary, that is to say, does not produce polypbuds, but only medusa-buds, from the first (Corymorpha, fig.
In this way the hydroid colony becomes composed of two portions of different function, the nutritive " trophosome," composed of non-sexual polyps, and the reproductive " gonosome," composed of sexual medusaindividuals, which never exercise a nutritive function while attached to the colony.
- Polyps from a Colony indicated in the case of the polyps of Hydractinia, magnified.