XV 
They are seen on primitive, secondary, and other 
rocks, sometimes on stems of coral, or on blocks 
of lava, on fragments of vases* and even on human 
skulls, which are exhibited in museums. Sometimes 
these Polypidoms wholly envelope the wood that 
floats upon the water ; at other times they surround 
and bury the fragments of wrecks, and the old vessels 
that are abandoned in the ports ; in fine, there are 
some whose base, dividing into numerous fibres like 
those of a root, penetrates deep into sandy or muddy 
shores to find a point of fastening which the surface 
cannot afford them. In general their base is solid or 
extended in the corticiferous Polypidoms ; fibrous in 
the calciferous ; and non-existing, or almost so, in the 
carnoid Polypidoms and the celluliferous. Thus, as 
this part only serves the Polypidom to fix itself, we 
may consider it as a means employed by Nature to 
prevent these beings, deprived of locomotion, from 
becoming the sport of the waves ; in this respect only 
they resemble vegetables. 
DURATION. 
All organized beings have three epochs of existence 
—their growth, their perfection, and their decline— 
both among the animal and the vegetable world 
