ORGANIC AGENCIES. 95 



if they remain attached, then a compound animal is 

 formed,, composed of many individuals, united together 

 precisely as a tree is formed of many buds, each of which 

 is in some sense an individual, and capable of independent 

 life. In the compound coral each bud has its own tenta- 

 cles, mouth, stomach, partitions, and other organs neces- 

 sary for life, and yet all are organically connected, and 

 each feeds for all. There is, therefore, a sort of individ- 

 uality in the aggregate, but a more decided individuality 

 in each bud. 



The form of the aggregate depends on the mode of 

 budding. If the buds grow into branches, then there is 

 formed a tree-coral (Fig. 48) ; but if the buds do not 



FIG. 48. Madrepora, a tree-coral. 



separate, but remain connected to their ends, and form 

 new buds in the intervening spaces, then they form a head- 

 coral (Fig. 49). There are all gradations between these 

 extremes. Coral-trees are often six to eight feet high, so 

 that one may literally climb among the branches. Coral- 

 heads form hemispherical masses fifteen to twenty feet in 

 diameter. In either case the aggregate consists of hun- 

 dreds of thousands of individuals ; in either case, also, 

 the living organic matter is confined to the superficial 

 portion, one quarter to one half an inch thick. As in 



