THE MEDUSA. 143 
The name of Hydrostatics or Hydromeduse@ is given to certain 
animals of this class which are essentially voyagers. They possess 
one or more air-vessels, little natatory bells of various forms. The 
elegant creatures frequently float on the waves, even when the 
howling tempest has lashed them into foam, like frail barks over- 
taken in a storm. But the sea may rage, the hydromedusa can 
never be submerged; nothing can force it beneath the surface. 
These acalephz have generally grey tentacles or fishing threads, of 
VELELLA. 
(Velella limbosa.) 
different lengths, and often very numerous and of great fineness. 
Their vessels or their bells hold them up in the water; their 
tentacles direct them in their movements; their fishing threads 
serve them at the same time for means of defence, for arms where- 
with to seize their prey, and for organs of suction. The hydro- 
meduse are compound animals, a kind of travelling polypier. 
Their colonies form fringes, garlands, and clusters of beautiful 
elegance. They are often composed of three kinds of elementary 
animalcules: those which are nurses; those which bear young, 
but have no mouth; and a third class, which are both progenitors 
and protectors of their offspring. 
These curious animals consist of a large bladder which contains 
all their organisation, or of floating bell-shaped bodies, which are 
