MORPHOLOGY OF THE MADREPORARIA. 



93 



pair of first cycle mesenteries, and it might be supposed that the 

 new mesenteries would occupy the exocoeles in regular succes- 

 sion from one aspect of the polyp to the other. Instead of this 



in 



in 



FIG. Sc. 



the pairs are found to arise successively within only the dorsal 

 member of the two exocoeles of each system. This is shown 



FIG. 8J. 



in the next stage available, Fig. S, where a third cycle pair is 

 found within the dorsal exocoele of each sextant. 



