242 THE OCEAN WORLD. 
that swims about.in the sea, many of them having a muscular motion 
as they swim along ;” these motions being effected, as he tells us in 
another place, by means of the pinnules or feather-like fins, “ evi- 
dently designed by Nature to-move the animal backward or forward 
in the sea.” Cuvier tells us they have 
' the power of moving by the contraction 
of the’ fleshy part: of the polypidom, 
and. ‘also by the combined action of 
its polpys. Dr. Grant says, “A more 
singular .and: beautiful spectacle could 
scarcely be ‘conceived than that of a 
deep purple P. phosphorea with all its 
delicate transparent polypi expanded, 
and emitting their usual brilliant phos- 
phorescent light, sailing through the 
still and dark abyss, by the regular and 
synchronous. pulsations of the minute 
fringed arms of the whole polypi;” 
while’ Linnzeus tells us that “the phos- 
phorescent. sea-pens which cover the 
bottom of the ocean cast so''strong a 
light, that it is easy to count the fishes 
and worins of various kinds meh sport 
among them.” 
Lamarck, Schweleser ad other 
naturalists, however, reasoning from 
what is known of other such animals, 
deny them the existence of this locd- 
motive power; ‘and there is little 
doubt,” says Dr. Johnston, “that these 
authors are right, for, when placed in 
a basin of sea-water, the Pennatule are 
‘never observed to change their position ; 
Fig. 97.—Sea-pen, Pennatula spinosa. they remain in the same spot, and lie 
ote y 0 CEdee ay with the’same side up or down, just ‘as 
they have been placed. ' They inflate 
the. body until it “becomes toa considerable degree transparent, and 
only streaked with intercepted: lines’ of red, which distend at one 
place and contract at another; they spread out the’ pinna, and the 
polyps expand their tentacula, but they never BHCHIPE to swim, or 
perform any process of locomotion.” ' 
Mr. Darwin's description of a kind of .Sea-pen, Virgularia Patt 
