CHAPTER XIY. 
Jelly-Fish, Corals, and Sea-Anemones,— 
Subkingdom CCELENTERATA. 
Few have been able to revel in the exquisite beauty of the southern coral islands, 
which through thousands of years have been slowly piled up to the surface of 
the water by the coral-animals. The vivid colouring of the fauna in the 
lagoons of those marvellous islands is not to be found in European seas, but even 
in these less favoured climes, any observant traveller, as his ship passes through 
calm water, may notice lovely creatures nearly related to the corals. Who, for 
instance, has not seen exquisitely coloured transparent jelly-fish, floating just below 
the surface, and propelling themselves by alternately expanding and contracting 
their bells ? Or who that has kept a marine aquarium has not admired, as its 
greatest ornament, the sea-anemones ? These animals, the corals, the jelly-fish, and 
the sea-anemones, constitute the great group known as Coelenterata. The group 
comprises all those creatures in which the internal cavity, corresponding with the 
alimentary canal of other animals, is not a closed canal running through the body, 
but is commensurate with the whole cavity of the body. Consequently there are 
no spaces answering to the body-cavity of the Yertebrates, between the wall of the 
alimentary canal and the outer wall of the body. 
A study of the earliest growth of the Ccelenterates has shown that their 
internal cavities are nothing more than regular radiate outgrowths of the intestine, 
and, like the latter, come from the primitive intestine of the larva. The result of 
this development is a condition which does not occur elsewhere in the whole animal 
kingdom. We have no separate digestive canal, no closed blood vascular system, 
and no specialised respiratory apparatus. There is only a system of cavities, all 
in open communication with one another, occupying almost every corner of the 
body. 
Again, the Coelenterates are radiate in structure, that is, when seen from above, 
they are typically star-shaped; and if a Coelenterate be cut across, every horizontal 
section shows a symmetrical arrangement of the parts around a centre. There are 
other radiate animals, such as the Echinoderms, but while in these five is the 
fundamental number of rays, in the Coelenterates the rays are often far more 
numerous, being some multiple of four or six. Again, while the skin of the former 
is almost always modified into a skeleton, or is thick like leather, leathery skins are 
the exception in the latter. When the Coelenterates do form calcareous skeletal 
structures, these are quite different from the tests of the sea-urchins; and, in all 
cases, the anterior end of the body, crowned with one or more circles of tentacles, 
remains soft and flower-like. The most highly developed of the free forms, how- 
