SUBKINGDOM 



CCELENTERATA. 



In this division of the animal reahn radial symmetry is more 

 marked tlian in Ecliinodermata. Its members are distinguished 

 from the latter division and from all higher animals by the more 

 simple structure of tlie body. They have no true separate stom- 

 ach, tlieir digestive cavity being, as in the " Jelly-fishes " simply 

 the general body-cavity, or in the higher forms, as the sea-anemone, 

 a more or less distinct portion of that cavity ; but in all cases the 

 "stomach" freely communicates with the body-cavity. The 

 animals are virtually digestive sacs. They have no circulating 

 organs, the nourishment being distributed by diverticula of the 

 general cavity. A water- vascular S3'stem is sometimes present. 

 Hollow tentacles, communicating witli the somatic cavity, fre- 

 quently surround the mouth, and are prehensile organs. A ner- 

 vous system may be entirely wanting, or represented by scattered 

 nerve cells, or at the best by a ganglionated ring. There are two 

 fundamental layers of tlie body wall, an inner layer, endoderm, 

 and an outer layer, octoderm. Reproduction is largely non- 

 sexual, or by budding. Defense is by means of "nettle-cells" 

 (cnidae). 



This division embraces the greater nujnber of animals popu- 

 larly called Zoophytes, and the producers of " coral," and is 

 divided into Actinozoa and Hydrozoa. 



CLASS ACTINOZOA. 



This class is wholly marine, and comprises the Sea-anemones, 

 Coral-polyps, Sea-pens, &c. They have a digestive sac which 

 opens below into the general somatic cavity. The space sur- 

 rounding the stomach— lying between it and the body wall, is 

 divided into vertical compartments by septa (mesenteries) spring- 

 ing from the outer wall. To the free edges of some of these 

 partitions the reproductive bodies are attached, which are thus 



