It is sufficient to state here that the medusa is usually a free-swimming animal, floating mouth downwards on the open seas, but in some cases it may be attached by its aboral pole, like a polyp, to some firm basis, either temporarily or permanently.
As already stated, a medusa of this order may be free-swimming or sessile in habit.
It is a top-shaped, free-swimming organism provided with a preoral band of cilia,.
A, The free-swimming embryo.- B, A sporocyst containing young rediae.
With the exception of a number of forms in which the whole development takes place within the egg or in the body of the mother, batrachians undergo metamorphoses, the young passing through a free-swimming, gill-breathing period of considerable duration, during which their appearance, structure, and often their regime, are essentially different from those of the mature form.