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.
The medusa which this hydroid liberates is called Thaumatias diaphana.
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.