PHYLUM COELENTERATA 



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. — Metridium marginatum, a sea-anemone, partly cut away so as to 

 show its structure. /, 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; q, outer ostium; 10, primary mesentery; 11, muscle-band on primary 

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

 tertiary mesentery; 75, quaternary mesentery; 16, reproductive gland; 17, 

 mesenterial filament; iS, 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, 9, 8) in these mesenteries. Smaller 

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



