136 THE ANIMALS AND MAN 



threads, which lie coiled up in small pockets until prey is 

 captured, when they uncoil, shoot out, and sting. If Hydra 

 catches an animal too large to be crowded into its mouth 

 it releases it. 



Note that Hydra can contract its tentacles and its whole 

 body until it looks like a small egg with a rosette of short 

 blunt fingers at one end. Sometimes Hydra may be seen 

 with another much smaller one growing out from it (fig. 55). 

 This is a new one, forming by the process of "budding." 

 It will grow and develop until about as large as the parent, 

 when it will break off, and attaching itself elsewhere will 

 begin an independent existence. Hydra has the interesting 

 power of being able to regenerate itself if cut in two. In 

 such a case each half will usually develop into a new com- 

 plete Hydra. 



Sea-anemones, corals and jellyflshes. — The sea-anemones 

 which are common in tide-pools, and the coral animals 

 which live in tropic and sub-tropic oceans, have the same 

 type of body as that shown by Hydra, but are much larger. 

 When the tide is out, exposing the dripping seaweed-covered 

 rocks, and the little basins are left filled with clear sea- 

 water, the brown and green and purple "sea-flowers" 

 may be seen fixed to the rocks by the base, with the 

 mouth opening and circlet of slowly moving tentacles 

 hungrily ready for food. Touch the fringe of tentacles 

 with your finger-tip and feel how they cling to it. If it 

 were a small animal, like a sea-snail, these deadly ten- 

 tacles would hold it fast and slowly carry it into the 

 mouth. Inside the body is a cylindrical hollow, which is 

 really a primitive kind of stomach. But there is no heart 

 nor brain nor lungs in this simple body. It is only a 

 thick-walled sac, with the mouth surrounded by food- 

 catching tentacles. 



The coral animals, or coral polyps, are simply a kind 

 of sea-anemone which secretes in its otherwise soft body- 



