1 8 THE SEAS 



common in the sea ; some are minute scraps of living matter, 

 such as the marine amoebae, quite unprotected and moving 

 about on the sea bottom by a kind of flowing motion ; 

 others possess elaborate little shells of limy matter and are 

 called Foraminifera, or of silica and are known as Radi- 

 olarians, both occurring in countless numbers in the surface 

 waters. Others again, called Ciliates, though without 

 shells, are of more complicated structure, being covered 

 with fine hairs by the beating of which they move and draw 

 m food. As widespread near the surface as the Radi- 

 olarians and Foraminifera, are the Dinoflagellates or 

 Peridinians which have two whip-like processes for loco- 

 motion, may or may not be covered with skeletal plates, and 

 often contain green colouring matter so that it is uncertain 

 whether they are animals or plants. 



The sponges or Porifera are animals of so simple a 

 structure that they give the impression of being little more 

 than aggregations of Protozoans. They are always attached 

 and have a supporting skeleton, of horny matter in the 

 sponge of commerce, but in the majority of cases consisting 

 of immense numbers of tiny spicules of many beautiful 

 shapes and formed in some cases of limy material and 

 others of silica. 



The Cxelenterata include a large number of relatively 

 simple animals whose bodies are essentially bag-shaped, 

 containing only one cavity which combines the functions 

 of the stomach cavity and the general body cavity of the 

 remaining, more highly-organized, animals. They are all 

 built on a circular plan, i.e. there are not two symmetrical 

 sides. They are almost entirely marine and are universally 

 distributed. They include many common animals and 

 ma3>- be said to be of two general types, attached like the 

 sea anemones, and freely swimming like the jellyfish. 

 Many of the attached kinds are not solitary individuals 



