26 CORALS AND CORAL ISLANDS. 



a kind of case or jacket, into which the upper extremity, 

 which is soft and delicate in texture, may be retracted. The 

 thickening of the epidermis in this middle portion is produced 

 through the entang-linsr of disintegrated cells and minute for- 



ACTINIA. 



eign particles, sometimes in part spores of Confervse, by- 

 means of the mucus of the surface ; and if the layer is re- 

 moved, as it may be, the skin will again become covered. 

 This species, like others of the genus, lives buried to its neck 

 in the sand, that is, with the soft upper extremity protrud- 

 ing. If disturbed, the head is suddenly drawn in, together 

 with more or less of the following jacketed part of the body. 

 The warty prominences on some warty species have the 

 power of clinging by suction to a surface, and such Actiniae 

 often coyer their sides thus with bits of shell or of other sub- 

 stances at hand. Where there are no warts the contracted 



