OTHER CCELENTERATA 



279 



typical instances, the life cj'cle of a scyphozoan consists of an 

 alternation of generations with an attached generation from which 

 the free-swimming jellyfish arises by budding that is transverse 

 to the long axis of the body. By this means saucer-like individuals 

 are produced, become detached, and grow into adult jellyfishes. 



Fig. 135. — Two divergent types among Coelenterata. 



Left, a Bpa-walnut, Hormiphora plumosa, a representative of the Class Ctenophora, 

 illustrating one of the types of delicate-bodied, free-swimming coelenterates. c, comb or 

 swimming plate, a row of very large cilia; m, mouth; s, sense organ; I, tentacle. (After 

 Chun.) 



Right, the sea anemone, Metridium dianlhus, a representative of the Class Artinozoa, 

 illustrating a heavy-bodied, attached type of ccelenterate. (Photo, of Jewell Model, by 

 courtesy of the General Biological Supply House, Chicago, 111.) 



The Actinozoa are represented by the familiar sea anemone, 

 Metridium dianthus (Fig. 135), of the New England Coast, and by 

 the true corals (Fig. 136) which abound in tropical seas. The latter 

 are like small sea anemones to which a skeleton of carbonate of 

 Ume has been added and which have budded to form colonies con- 

 taining innumerable individuals. The part that has been plaj^ed 

 by corals in the formation of coral islands and the coral limestone 

 of various geologic formations has given these coelenterates an 

 important role in the history of some portions of our planet. 



