THE FLOWER- ANIMALS. 1 43 



and is more especially represented in the warm seas by an 

 abundance of beautiful and highly-coloured forms like 

 flowers. Hence they are also called Flower-animals 

 (Anthozoa). Most of them are attached to the bottom 

 of the sea, and contain an internal calcareous skeleton. 

 Many of them by continued growth produce such im- 

 mense stocks that their calcareous skeletons have formed 

 the foundation of whole islands, as is the case with the 

 celebrated coral reefs and atolls of the South Seas, the re- 

 markable forms of which were first explained by Darwin. ^^ 

 In corals the counterparts, or antimera — that is, the cor- 

 lesponding divisions of the body which radiate from and 

 surround the central main axis of the body — exist some- 

 times to the number of four, sometimes to the number of 

 six or eight. According to this we distinguish three legions, 

 the Fourfold (Tetracoralla), Sixfold (Hexacoralla), and Eight- 

 fold corals (Octocoralla). The fourfold corals form the 

 common primary group of the class, out of which the six- 

 fold and eightfold have developed as two diverging branches. 

 , The second class of Sea-nettles is formed by the Hood- 

 jellies (Medusae) or Polyp-jellies (Hydromedusse). While 

 most corals form stocks like plants, and are attached to 

 the bottom of the sea, the Hood-jellies generally swim about 

 fieely in the form of gelatinous bells. There are, however, 

 numbers of them, especially the lower forms, which adhere 

 to the bottom of the sea, and resemble pretty little trees. 

 The lowest and simplest members of this class are the 

 little fresh-water polyps (Hydra and Cordylophora). We 

 may look upon them as but little changed descendants of 

 tliose Primoival polyps (Archydrse), from which, during the 

 primordial period, the whole division of the Sea-nettles 



