AGE OF COBAL REEFS. 193 



periority of the single ones and of those that 

 grow in communities. When the little Polyp 

 Coral, the Astraean or Madrepore, for instance, is 

 born from the egg, it is as free as the Actinia, 

 which remains free all its life. It is only at a 

 later period, as its development goes on, that it 

 becomes solidly attached to the ground, and be- 

 gins its compound life by putting forth new 

 beings like itself as buds from its side. Since 

 we cannot suppose that the normal development 

 of any being can have a retrograde action, we 

 are justified in believing that the loss of freedom 

 is in fact a stage of progress in these lower 

 animals, and their more intimate dependence on 

 each other a sign of maturity. 



There are, however, structural features by 

 which the relative superiority of these animals 

 may be determined. In proportion as the num- 

 ber of their parts is limited and permanent, their 

 structure is more complicated ; arid the indefi- 

 nite multiplication of identical parts is connected 

 with -inferiority of structure. Now in these low- 

 est Polyps, the Actiniae, the tentacles increase 

 with age indefinitely, never ceasing to grow while 

 life lasts, new chambers being constantly added 

 to correspond with them, till it becomes impossi- 

 ble to count their numbers. Next to these come 

 the true Fungida3. They are also single, and, 

 though they are stony Corals, they have no share 



