CORAL-MAKING POLYPS. 23 



Cerianthus of the Philippine Islands, with its thread-cells, 

 builds a sheath or leathery tube one foot four inches in 

 length, that is sunk into the mud. 



Development. Anemones multiply by budding, or, if 

 pieces of the disk are cut or torn off, they will grow into 

 anemones. They also deposit eggs, the young being at 

 first free swimmers, by means of cilia, finally becoming 

 fixed upon the bottom, and assuming the adult form. 



NOTE. In their habits they are remarkable. One observed by 

 Dr. Collingwood in the China Sea was two feet in diameter, giving 

 shelter in its stomach to a little fish, that, when danger approached, 

 rushed into its protector, whose tentacles closed up like a door. A 

 fish, known as Premnas biaculcatus, also lives within the stomach of 

 the anemone, Actinia crassicornis. Some live a roving life, like the 

 Adamsia, that is often found upon the back of the hermit-crab, that, 

 upon leaving its shell, obliges its friend, the anemone, to change also. 

 The Urticina is luminous. 



VALUE. The anemones are great purifiers, and are eaten in vari- 

 ous parts of the world. 



Coral-making Polyps. The coral animal may be 

 considered an anemone that has the power of secreting 

 lime. In the star-coral (Astrea), the young is seen at the 

 end of June a little oblong-shaped body, swimming about 

 by its cilia, or oars. It soon attaches itself to the bottom, 

 and, if in a few days it should be removed, there would 

 be found a little platform with radiating partitions of lime 

 alternating with the soft ones that we have seen in the 

 anemone. If allowed to grow, tentacles soon appear ; 

 other small partitions are now secreted, that extend to 

 the outer wall, which is also being secreted ; and, finally, 

 we have a coral polyp, from which others branch, until 

 large blocks are formed of many individuals, but all con- 

 nected. So it will be seen that the polyp is not an insect, 

 neither does it erect or build its house any more than a 

 man builds his skeleton, but is a lime-secreting animal, 

 pure and simple. 



