44 



CORAL, BY MARGARET L. KINGSBURY. 



The coral polyp is somewhat like a jelly-fish, but is very much smaller, 

 sometimes not being larger than the head of a pin. The structure of the 

 polyp consists of a cylindrical, or sack-like, membrane attached at the bottom 

 to some solid body, and inclosing a second sack, which forms the stomach. 



At the top is an opening, or mouth, which is surrounded by thread-like 

 organs, called tentacles. They are all hollow, and open into the body, which 

 is also hollow. 



The polyp gets its food by these tentacles in this manner ; there are 

 always things floating around the water which they can use for food. By 

 the sixth sense they know when it comes within their reach, they then reach 

 out a little feeler from the tentacle nearest the object, and in a sense para- 

 lyze it, grasp it and throw it into its mouth, from whence it passes into the 

 stomach. 



Fig. 22. 



A, Erain Coral, B, Branching; E Elliptical. 



It breathes by passing water into a cavity, next to the outer skin of its 

 body, which is divided into partitions, all radiating from a common centre : 

 the air which the water carries is passed from one little room to another and 

 enables it to breathe. 



The coral docs not grow in water over one hundred and fifty feet deep. 



The polyp is always taking in carbonate of lime, which passes through 

 them, and goes to build up the skeleton to which they are fastened, and 

 which grow until they reach the top of the water, when they die, for 

 coral polyps cannot work out of water. 



As the growth of coral becomes larger, the polyps on the outside be- 

 come stronger than those inside, the latter ones die, and the coral sinks in 

 the middle so much that when it reaches the surface, it is usually in the 



