CCELENTERATA AND PORIFERA 



175 



to the rocks and wharves a short distance beneath the sur- 

 face of the water. They vary in diameter from a fourth 

 of an inch to two 

 feet. Themoment 

 they are disturbed 

 the numerous ten- 

 tacles around the 

 mouth are con- 

 tracted, and the 

 fleshy mass be- 

 comes a brown 

 conical body. 



The coral polyp 

 is similar to the 

 anemone, but much 

 smaller. It secretes 

 from the sea water 

 lime which is de- 

 posited throughout 

 its tissues to form 

 a skeleton. Most 

 corals, like the hydroids, bud freely and thus great masses 

 of coral are formed. They dwell only in the warmer parts 

 of the ocean. 



Porifera: Sponges 



The sponges are mostly ocean dwellers, only about thirty 

 species being found in fresh water. A simple sponge, such 

 as Grantia or Leucoselenia, growing near the surface of the 

 water on logs and stones along the Atlantic coast, has 

 much the same structure as Hydra, but the walls composed 



FIG. 205. Coral. Each of the two thousand or 

 more small projections is the work of one coral 

 polyp. Photograph, one third natural size. 



