FRESH-WATER POLYP AND SOME ALLIES 277 



crown of many small, slender tentacles. At the middle of 

 the oral surface is the mouth, which is a slit-like open- 

 ing. The skin of the body is soft, but it is rather tough. 



Fig. 146. Dissection of a sea anemone. (Natural size) 



1, zone between tentacles and mouth; 2, lip; 3, ciliated groove in gullet ; 4, gul- 

 let ; 5, inner end of gullet ; 6, edge of mesentery ; 7, cavity within tentacle ; 

 8, 9, internal openings between chambers; JO, primary mesentery; 11, muscle 

 of primary mesentery; 12, abnormal tertiary mesentery; 13, secondary mesen- 

 tery; Ik, tertiary mesentery; 15, quaternary mesentery; 16, gonad; 17, mes- 

 enterial filament; 18, opening for mesenterial filament 



The mouth opens to receive the food, which is sometimes 

 quite large, and the gullet (Fig. 146, 4) passes it down by 

 ciliary action aided by muscular activity in the gullet- wall. 

 At the inner end (Fig. 146, 5) of the gullet, food passes into 



