POLYPI. 



147 



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). i 



57 



Polypi form a very extensive order of zoophytes, 

 abounding in every part of the ocean, but growing 

 in greatest luxuriance in the warmer regions of 

 the globe. Their flesh exhibits the same granular 

 appearance as that of the sponge, but it is generally 

 firmer, and often intermingled with masses of cal- 

 careous matter. The tentacula, which may be 

 compared to arms, vary in number and in length 

 in different species of polypi, and sometimes, in- 

 stead of a single row, each of the mouths has two 

 or more series of tentacula placed around it. They 

 are formed of a prolongation of the soft substance 

 of the polypus, and are usually tubular ; and 



* The Hydra sociata of Gmelin ; the Actinia sociata of Elhs. 

 t In this figure two hydrae are seen attached to the stem of a 

 plant. 



