ORGANIC AGENCIES. 



93 



the lower end of the stomach is the pylorus, which may 

 be opened and shut like a second mouth. Eunning from 

 the outer wall, and converging toward the axis, are many 

 partitions, p p f some of which reach the stomach and 

 hold it steadily in the axis, but below the stomach termi- 

 nate in free, scythe-like edges. These converging par- 

 titions divide the body cavity into a number of trian- 



FIG. 45. Ideal section, vertical and horizontal, showing structure : t, tentacles ; 

 #, stomach ; ^;, p, partitions. 



gular apartments, which, however, are in free communi- 

 cation with each other below the stomach. Besides the 

 main partitions spoken of, there are very many smaller 

 ones which do not reach so far as the stomach. The 

 whole structure may be briefly summarized by tracing the 

 course of the food. Food is taken by the tentacles, put 

 into the mouth, and passes into the stomach. After 

 digestion, whatever is refuse is thrown back through the 

 mouth, and the digested food is dropped through the 

 pylorus into the general hall below the stomach, and 

 there mixed with sea-water and circulated through all the 

 apartments. 



Simple Coral, or Stone Polyp. Now, a simple coral 

 has a similar structure, except that stony matter (lime 



