PHYLUM CCELENTERATA 



135 



stomodaeum and the body-wall, and open into a common basal 

 cavity. The six pairs of thin, double partitions between these 

 chambers are called primary septa or mesenteries (Fig. 84, 10; 



FIG. 84. Mftriditim marginatum, a sea-anemone, partly cut away so as to 

 show its structure. /, intermediate zone; 2, lip; j, siphonoglyphe; 4, gullet ; 

 5, inner end of gullet; 6, edge of mesentery; 7, cavity of a tentacle; 8, inner 

 ostium; Q, outer ostium; 10, primary mesentery; n, muscle-band on primary 

 mesentery; 12, abnormal tertiary mesentery; 13, secondary mesentery; 14, 

 tertiary mesentery; 15, quaternary mesentery; 16, reproductive gland; 17, 

 mesenterial filament; 18, opening for mesenterial filament. (Redrawn from 

 Linville and Kelly.) 



Fig. 85, p.m). Water passes from one chamber to another 

 through pores (ostia, Fig. 84, Q, 8) in these mesenteries. Smaller 

 mesenteries project out from the body-wall into the chambers, 



