SEA-PENS. I21 
With most polypiers the elementary individual, in spite of the 
adhesion established among the members of the colony, possesses 
a vital energy all its own, and is, in some respects, quite inde- 
pendent. Each has its own particular will, which may or may 
not be in harmony with the rest, and perhaps it is on account 
of this insurmountable difficulty that nature has rendered these 
creatures fixed and sedentary. Thus the polypes are prevented 
from attempting to exert any common will to move, like a single 
individual. It is not so with the sea-pens; their colony is 
not fixed and stationary; they move very little, it is true, 
yet they move. What do we conclude from this? That the 
parts which they possess in common, in place of being bony or cal- 
careous, and consequently insensitive, are fleshy, with contractile 
powers, and therefore capable of conveying sensation; consequently, 
the polypes of the sea-pens are less independent of each other 
than the coral polypes, having a central, perhaps a sensible organ, 
common to all, which binds them to each other, giving a certain 
unity to their acts. The coral polypiers have no will, those of the 
pennatula have. 
The fresh-water polypiers, which are true miniatures of the 
marine polypiers, are also not all fixed—some are capable of 
moving, thus in the ponds and streams we find little imperceptible 
creatures, analogous to the great wandering zoophytes which the 
waves nourish, and which float in the world of waters. 
