256 



GENERAL ZOOLOGY 



animals that do not have a body-cavity and an alimentary 

 canal have but one cavity to take their place ; this cavity is 



FIG. 129. Dissection of the Sea-Anemone (Metridium marginatum). 

 Natural size 



1, intermediate zone; 2, lip; 3, siphonoglyphe ; 4, gullet; 5, inner end of gullet; 

 6, edge of mesentery ; 7, cavity of a tentacle ; 8, inner ostium ; 9, outer ostium ; 

 10, primary mesentery; 11, muscle-plate on primary mesentery; 12, abnor- 

 mal tertiary mesentery ; 13, secondary mesentery ,- 14, tertiary mesentery ; 

 15, quaternary mesentery; 16, reproductive gland; 17, mesenterial filament; 

 18, opening for mesenterial filament. 



called the gastrovascular cavity, because in the same space 

 food is digested and carried about. The fact that food and 

 oxygen can pass into any portion of the body, even into 



