A striking influence of gravitation can be observed in a hydroid, Antennularia antennina, from the bay of Naples.
The hydroid Zoophytes are represented in the first plate by the following examples.
A hydroid about one inch high, growing in patches and appearing like tufts of moss on rocks between tide-marks.
There are some species which, having no hydroid or strobila state, mature without alternation of generation (metagenesis).
You see the hydroid does not in the least resemble a jelly-fish.
The hydroid Hydractinia polyclina often covers the exterior of such shells with a brown, velvety growth.
Tubularia (fig. 4), a well-known British hydroid, bears gonophores.
In Fig. 78 we have a portion of the hydroid stock from which this Jelly-fish arises, also greatly magnified.
Hydra is, moreover, bisexual, in contrast with what is known of hydroid colonies.
There are kinds of jelly-fish that produce jelly-fish and have no hydroid stage at all.
Any of numerous, usually colonial marine coelenterates of the order Hydroida, having a polyp rather than a medusoid form as the dominant stage of the life cycle. Hydroids have a simple cylindrical body with a mouthlike opening surrounded by tentacles. Most species form colonies with individual hydroids branching off from a common hollow tube that is probably used to share ingested food. The young develop from eggs or from buds. The most well-known hydroids are the hydras (genus Hydra), which are atypical in being both freshwater and solitary.