Medusa-buds) in the extreme of degeneration, then it follows from Brooks's theory that Hydra must be descended from an archaic form in which the medusan type of organization had not yet been evolved.
They are for the most part marine in habitat, but a familiar fresh-water form is the common Hydra of ponds and ditches, which gives origin to the name of the class.
Hence only the genus Hydra can be considered as truly representing the order Eleutheroblastea.
Hydra must, in short, be a living representative of the ancestor of which the actinula-stage is a transient reminiscence in the development of higher forms. It may be pointed out in this connexion that the fixation of Hydra is only temporary, and that the animal is able at all times to detach itself, to move to a new situation, and to fix itself again.
After crossing the Hydra - 6 tes (Ravi) he once more came into contact with hostile tribes, and the work of storming petty towns began again.
Protohydra is a marine genus characterized by the absence of tentacles, by a great similarity to Hydra in histological structure, and by reproduction by transverse fission.
In Hydra viridis the polyp is of a green colour and produces a spherical egg with a smooth shell which is dropped into the mud.
To complete our survey of life-cycles in the Hydromedusae it is necessary to add a few words about the position of Hydra and its allies.
The month of April had witnessed the revolt of the principal Greek islands, Spetsae on the 7th, Psara on the 23rd, Hydra on the 28th and Samos on the 30th.
There is no difficulty whatever in regarding Hydra as bearing the same relation to the actinula-stage of other Hydromedusae that a Rotifer bears to a trochophore-larva or a fish to a tadpole.