CHAPTER XIV 



JELLYFISH, CORALS, AND SEA ANEMONES 

 Subkingdom CCELENTERATA 



FEW have been able to revel in the exquisite beauty of the southern coral is- 

 lands, which through thousands of years have been slowly piled up to the surface 

 of the water by the coral animals. The vivid coloring of the fauna in the lagoons 

 of those marvelous islands is not to be found in European seas, but even in these 

 less favored climes, any observant traveler, as his ship passes through calm water, 

 may notice lovely creatures nearly related to the corals. Who, for instance, has 

 not seen exquisitely colored transparent jellyfish, 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 jellyfish, 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 Vertebrates, between the wall of the alimentary canal and 

 the outer wall of the body. 



A study of the earliest growth of the Coelenterates has shown that their in- 

 ternal 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 specialized 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 Ccelenterate 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 nu- 

 merous, 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- 

 ever, such as the sea anemones and the jellyfish, have no hard skeleton at all, but 

 are among the most delicate and beautiful objects in the realm of living nature. 

 (3448) 



