ON POLYPI. 587 
As for the composing polypi, each of them, without doubt, 
must grow. But the truth is, all is conjecture here, nor is 
our knowledge of the habits of the pennatule at all adequate 
to assist us in throwing light on these very difficult points of 
physiology. 
‘ The pennatule, as it seems, live constantly in the high 
seas, and are always floating. Although they are in a conti- 
nual movement of systole and diastole, somewhat like the 
medusz, which is produced by the contraction of the inflated 
and posterior part of the animal, and especially by the wing- 
lets, or polypiferous branches, it is not probable that they 
possess the least power of directing themselves in the inte- 
rior of the waters. 'They are altogether under the influence 
of the currents, like the meduse themselves. Still less is it 
admissible that the composing polypi can conspire toge- 
ther in their movements, to direct themselves in determinate 
tracks. This is an hypothesis which defies conception, nor 
is the object of such a faculty at all perceptible. Hach poly- 
pus acts independently of its neighbour, and the object of the 
motion of its tentacula, is only to seize the little animals which 
may come within its reach. 
Pennatule have been observed in every sea, but their known 
species are not numerous. 
We shall dismiss the consideration of this class, with a 
notice of the SPONGES (spongia ). 
This is a group of organized bodies, extremely extended in 
every sea, but particularly in those of warmer climates. ‘They 
have been known since the remotest antiquity, and, never- 
theless, naturalists are far from being agreed with respect to 
their true character. Some will have them to be vegetables ; 
others a wholly simple animal; and several, polyparia, of 
which the animal is unknown. All the authors of antiquity 
allowed them a sensitive life, and admitted that the living 
sponges seemed to avoid the hand which would touch them, 
