RADIATES. 



345 



repore were spoken of as blossoms of stony plants. It 

 is now about a century since their animal character was 

 really admitted by naturalists ; and it is only quite re- 

 cently that their structure and habits have been thor- 

 oughly investigated. 



599. The Polypes, or Zoophytes, have the most simple 

 construction of all animals, but they differ from each oth- 

 er in the degree of their simplicity. The most simple of 

 all are the Hydras little Polypes which you can find in 

 stagnant waters. In Fig. 270 you have a representation 



of one of these. The smaller 

 figure shows it of the natural 

 size. It is a simple sac or 

 purse-like animal, with a mouth, 

 and tentacula arranged around 

 the mouth. With these tenta- 

 cles or arms the animal catches 

 its prey, and puts it into its 

 stomach through the mouth, a. 

 In its general shape, and in the 

 working of the arms, it is much 

 like the Cuttle-fish ( 550). Its 

 tentacles are, however, armed 

 in a very different manner. 

 They have neither suckers, like 



Fig. 270.-Hydra. t ^ ose Q f t ^ e Cuttle-fish, nor cil- 



ia, like those of many animals, but minute bristles, and 

 sharp, firm spines, curiously arranged. These spines are 

 concealed in wart-like processes when they are not in 

 use, but they can at any time be thrust out, just as the 

 claws of a carnivorous animal are protruded from their 

 concealment when their services are needed. 



600. When the Hydra is searching for prey, it allows 

 its tentacles to float about in the water, its body being 

 fastened by a sucker to some solid substance. If a Crus- 

 tacean or an aquatic worm happens to hit one of them, 

 the arm is immediately thrown around it, as you see in 



P2 



