172 SYSTEMATIC ZOOLOGY. 



the individual polyps, but the division does not affect the 

 digestive tract, so all are connected, and the food which is 

 taken in at one mouth may serve to nourish any part of 

 the whole colony (fig. 18). In some the outer surface 

 of the body is naked, but in many of the solitary and in 

 most of the colonial forms the base or both base and 

 column secrete carbonate of lime, thus forming a solid 

 support for the body. This solid support is the well- 

 known coral. In most specimens of coral one can readily 

 recognize the cups (fig. 19) in which the separate polyps 

 were situated; and in these cups, in most cases, are calcare- 

 ous partitions much like the septa of the soft parts.* As 

 long as the colony remains alive it is constantly budding 

 off new polyps, and thus the colony and the coral grow. 

 Those species which live in cold water produce but little 

 coral, but in tropical waters coral-producing forms abound, 

 and by their combined secretions the coral islands are 

 made. 



The great majority of the Actinozoa may be subdivided, 

 according to the number of septa, into two orders: 



ORDER I. OCTOCORALLA. 



In these the separate polyps are small, and each has but 

 eight septa and eight tentacles. They produce but little 

 coral, but rather those kinds of coral which are known as 

 sea-fans and sea-whips. One form is especially notice- 

 able, since it produces the precious red coral so often carved 

 into beads, etc. 



* These calcareous septa do not coincide with, but alternate in 

 position with, the fleshy septa. 



