198 THE BOTTOM OF THE SEA. 



terised by tlie continuity of each column down to 

 the base. The species of astrea are numerous, more 

 particularly in the neighbourhood of the equator. 



When the buds in the process of development do 

 not remain parallel with the mother-branch, the 



Fig. 38. — Astrea Punctifera. 



polypier takes the form of a tree, more or less dis- 

 tinctly. In this case, the name it bears recalls the 

 ve:^etable form to which it approximates. The 

 Madrepora jplantaginea (fig. 39) is formed by the 

 aggregation of small polypi joined together by masses 

 more or less conical in form. To every polypus there 

 is a corresponding little depression, surrounded with 

 a slight eminence. In general appearance the poly- 

 pier with its polyps resembles a spike of plantain. 



