Hydroid synonyms

The hydroid colony shows many variations in form and architec- ture which depend simply upon differences in the methods in which polyps are budded.

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.

Besides the three types of individual above mentioned, there are other appendages of hydroid colonies, of which the individuality is doubtful.

Such are the " guard-polyps " (machopolyps) of Plumularidae, which are often regarded as individuals of the nature of dactylozoids, but from a study of the mode of budding in this hydroid family Driesch concluded that the guard-polyps were not true polyp-individuals, although each is enclosed in a small protecting cup of the perisarc, known as a nematophore.