294 TOILERS IN THE SEA. 



The cell, or polype home (called scientifically 

 Zoceciuni), has a double cell-wall, enclosing the initial 

 polyzoon. The outer coat is a chitinous, or horny, 

 membrane, thickened and strengthened, in most cases, 

 by deposits of lime or flint, then forming a solid wall, 

 externally often ornamented or embossed, but occa- 

 sionally it retains its membraneous character. The 

 colony consists of a number of these cells, attached 

 together in a variety of ways, but produced by con- 

 secutive budding, or gemmation, from the original 

 cell. Communication is maintained between the 

 several cells of the colony, through thin perforated 

 plates in the outer wall, called " communication- 

 plates." Through the minute perforations in these 

 plates thread-like connectors pass from animal to 

 animal, and thus all the polypes in a colony are linked 

 together. The function of this outer wall, then, is 

 the protection of the enclosed polype. 



The inner wall of the cell is a soft living mem- 

 brane, which lines the more or less solid outer wall, 

 and is supposed to be intimately associated with all 

 budding processes which subsequently take place. 

 It will be sufficient here to regard it as the soft lining 

 of the walls of the house which contains the living 

 Polyzoon. 



The animal is crowned with a wreath of tentacles, 

 which are seated on a circular disc, surmounting the 

 body, with the mouth in the centre (fig. 57). These 



