162 



THE MECHANICAL FUNCTIONS. 



nature of its internal texture. Each of the 

 polypes with which its surface is studded has 

 eight serrated tentacula. Fig. 57 represents one 

 of these polypes detached. Polypes may thus be 

 united in immense numbers in one mass, having 

 mutual organic connexion. In other cases they 

 may form smaller clusters, or be even totally 

 unconnected. Sometimes the detached polypes 

 are still disposed to assemble in groups, as is the 

 case with the Zoanthus of Cuvier* (Fig. 58): at 

 other times they are altogether isolated, as in 

 the Hydra viridis (Fig. 59). 



Polypi form a very extensive order of zoo- 

 phytes, abounding in every part of the ocean, 

 but growing in greatest luxuriance in the 



The Hydra sociata of Gmelin; the Actinia sociata of 



Ellis. 



