A cyst or sac of a siphonophore, containing environment and serving as a float.
A cyst or sac of a siphonophore, containing air, and serving as a float, as with Physalia.
The air-sac, float, or pneumatophore of an oceanic hydrozoan or siphonophorous hydromedu-san; one of the a few appendages of this stem among these organisms, offering to buoy all of them in liquid. See cuts under Athorybia and Hydrozoa.
In ornithology, an air-sac or air-space; among the cavities in a bird's human body full of air.