384 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



with similar boring habits, as well as comatulids attached to the sur- 

 face, all take advantage of the indraft of water into the small canals. 



The polyzoans, phoronids, rhabdopleurids, and cephalodiscids are 

 all provided with a tentacular apparatus, the tentacles being abun- 

 dantly 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 everywhere, are leaflike or encrust- 

 ing growths on seaweeds, etc. ; the individual animals in the colonies 

 are minute, but very numerous, and are often divided into various 

 types, each suited to perform a special function; A few polyzoans 

 are solitary, 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 bud- 

 ding from the same original individual and all live together in the 

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

 zoans and rhabdopleurids. 



The colonial tunicates or sea squirts form thick incrustations on a 

 usually rocky base. They are provided with an exceedingly fine 

 sieve through which they draw the water, separating out from it 

 the food particles. 



The colonial ccelenterates 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 seaweeds 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 of- 

 fered for sale. Other sorts of ccelenterates are the sea pens and sea 

 feathers, dead men's fingers and other alcyonarians, horny corals 

 or antipatharians, and the colonial anemones. All of the sea anem- 

 ones and jellyfishes belong to this group, and indeed many of tlie 

 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 portion consists only of 

 a relatively thin superficial layer. The stony axis of the red coral 

 is familiar to all because of its use in jewelry. Some ccelenterates 

 reach a very large size, certain gorgonians attaining a height of 15 

 feet, some sea pens being 6 or 7 feet or more in length, and some 

 umbellularians more than 8 feet tall. 



The colonial ccelenterates consist of a great number of sacklike 

 units which have about the opening a row of 6 or 8 or more ten- 

 tacles armed with formidable stinging organs, or of such units 



