2l6 ZOOLOGY 



medusa form independently. Some of them are of great 

 size, the disk or umbrella as much as 4 feet in diameter. 

 One specimen was found to weigh 90 pounds, but 

 of course this was mainly water. Large jellyfishes cast 

 up on sandy shores form only thin films when dried by 

 the sun. 



The sea 6. The typical anthozoan, as represented by the sea 



and* 16 anemone, is a more or less columnar animal, with the 

 relatives upper end furnished with numerous tentacles, which 

 serve for catching the prey. In the middle of the upper 

 surface is seen the mouth opening, which is usually more 

 or less oval or slitlike, giving the animal an incipient 

 bilateral symmetry. The mouth is the upper end 

 of the throat or stomodceum, the lower end of which 

 really corresponds to the mouth of the hydra. The 

 stomach cavity is not a simple sac, as in the hydroids, 

 but is invaded by a series of leaflike projections from 

 the sides, called the mesenteries. In the coral-forming 

 species the septa of the coral alternate with the mesen- 

 teries, and hence it is possible to determine to a con- 

 siderable extent what form the soft parts had in fossil 

 corals of vast antiquity. The Alcyonaria (Fig. 9, page 

 39) constitute a peculiar subclass of Anthozoa, in which 

 the individuals possess eight pinnate or featherlike ten- 

 tacles. All produce a limy so-called skeleton, and the 

 various remarkable colonial forms, as seen after the death 

 of the animals, resemble columns of basalt or other cu- 

 rious structures, little suggestive of anything living. It 

 is only by the careful study of the living creatures that 

 we can perceive their agreement with the ccelenterate 

 plan of organization. 



Coral 7- Coral reefs, produced by Anthozoa living in vast 



groups, are of great interest and importance to geog- 

 raphers and geologists. Innumerable islands of the 



