igefe) INVERTEBRATE ANIMALS. 
from. It is therefore owts¢de the polypes, and bears to the 
coenosarc the same relation that the trunk of a tree bears to its 
investing bark. This is well shown in fig. 39, 4, where there is 
represented one of these sclerobasic corals in which the coral- 
lum consists of alternate horny and calcareous joints. The 
polypes of all the Gorgonide agree, of course, with their order 
in having eight tentacles each, and by this they are distin- 
guished from the few Zoaztharia in which there is a sclerobasic 
coral. 
The best known of the Gorgonide is the Corallium rubrum, 
or “red coral” of commerce, which is largely imported from 
the Mediterranean. In this species there is a bright red, finely- 
grooved, calcareous sclerobasis, usually more or less repeatedly 
branched. The corallum is invested by a bright red coenosarc 
or bark, which is studded with numerous little apertures. The 
polypes can be protruded from these openings at will, and are 
milk-white in colour, with eight fringed tentacles each. The 
entire coenosarc is excavated into a number of communicating 
canals, with which the cavities of the polypes are connected, the 
whole system being filled with a nutritive fluid known as the 
‘angike: 
OrbDER III. RuGcosa.—This order merely requires mention, 
as all its members are extinct, and are therefore only known to 
us by their hard parts or skeletons. They agree with the Zoan- 
tharia sclerodermata in having a well-developed sclerodermic 
corallum, but differ from them in the fact that the septa are 
always some multiple of four (fig. 35, 4); and there are generally 
transverse plates or tabule combined with the vertical plates 
or septa. On the other hand, they agree with the A/cyouaria 
in having their parts in multiples of four, but differ from them 
in having a well-developed ‘sclerodermic corallum in which 
septa are present. They are chiefly known as fossils in the 
older rocks of the earth’s crust, and have hardly any representa- 
tives.at the present day. 
ORDER IV. CTENOPHORA.—The fourth and last order of the 
Actinozoa is that of the Ctenophora, comprising a number of 
free-swimming oceanic creatures, very different in appearance 
from any of the forms which we have hitherto been considering. 
They are all transparent, gelatinous, glassy-looking creatures, 
