THE SEA SHORES 1 75 



all are provided with a tentacular apparatus, the tentacles 

 being abundantly supplied with cilia which pick the food 

 particles from the water and pass them downward along their 

 inner side toward the mouth. The polyzoans, common every- 

 where, are leaf-like or encrusting growths on sea-weeds, etc. ; the 

 individual animals in the colonies are minute but very numer- 

 ous, and are often divided into various types each suited to per- 

 form a special function. A few polyzoans are sohtary or occur 

 in small colonies. The representatives of the other three groups 

 mentioned above are mostly uncommon, local, or inhabiting 

 rather deep water. In the phoronids and cephalodiscids the 

 individual animals in the colony, though they all arise by 

 budding from the same original individual and all Hve together 

 in the same mass of tubes, are not connected with each other 

 as in the polyzoans and rhabdopleurids. 



The colonial tunicates or sea-squirts form thick incrustations 

 on a usually rocky base. They are provided with an exceed- 

 ingly fine sieve through which they draw the water, separating 

 out from it the food particles. 



The colonial coelenterates are very diverse in size and shape. 

 The most familiar are the corals, millepores, red corals, and 

 sea-fans or gorgonians of the warmer seas, and on our coasts 

 numerous kinds of hydroids forming mossy or feathery plumes 

 on sea-weeds or on other objects. One of the last, dried, 

 stained green, and placed in a flower-pot, is the common 

 "Japanese air-plant" sometimes seen offered for sale. Other 

 sorts of coelenterates are the sea-pens and sea-feathers, dead- 

 men's fingers and other alcyonarians, horny corals or anti- 

 patharians, and the colonial anemones. All of the sea-anemones 

 and jelly-fishes belong to this group, and indeed many of the 

 smaller of the latter are nothing more than the sexual units 

 which have been liberated from hydroids. 



The stony corals are important in assisting to a greater or 

 lesser extent in the formation of the immense coral reefs which 

 are such a conspicuous feature in many parts of the tropical 

 seas. Some of them grow to a huge size, though the living 



