Note:  Do not rely on this information. It is very old.

Medusae

Medusae, the young of many forms of Hydrozoa (q.v.). They are bell-shaped organisms consisting of a hemispherical fleshy disc, from the centre of which hangs a soft tube, and the mouth opens at the free end of this, and leads to a large cavity, the atrium, from which radiate a number of gastric canals.