250 
COMPARATIVE ZOOLOGY. 
naria in its usually larger size and solid disk, four radiat¬ 
ing canals, which ramify and open into a circular vessel, 
running around the margin of the disk. 129 
Class II.—Anthozoa. 
These marine animals, which by their gay tentacles con¬ 
vert the bed of the ocean into a flower-garden, or by their 
secretions build up coral-islands, 
have a body like a cylindrical 
gelatinous bag. One end, the 
base, is usually attached ; the 
other has the mouth in the cen¬ 
tre, surrounded by numerous 
hollow tentacles, which are cov¬ 
ered with nettling lasso-cells. 
This upper edge is turned in so 
0 .. , A as to form a sac within a sac, 
Fig. 198.—Horizontal Section of Ac¬ 
tinia through the stomach, show- like the neck of a bottle turned 
ing septa and compartments. . . . . 
outside in. I he inner sac, which 
is the digestive cavity, does not reach the bottom, but opens 
into the general body-cavity (Fig. 38). 130 The space between 
these two concentric 
tubes is divided by a 
series of vertical parti¬ 
tions, some of which 
extend from the body- 
wall to the digestive 
sac, but others fall 
short of it. Instead, 
therefore, of the radi¬ 
ating tubes of the Aca- 
leph, there are radiat¬ 
ing spaces. No mem¬ 
bers of this class are 
. . . Fia. 199.— Actinia expanded, seen from above. 
microscopic. All are showing mouth. 
