4(32 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



The polyp from which tig. 8e was taken contains a like number of mesenteries, but the right 

 middle system includes only one pair of mesenteries, while the right ventral has two. 



ur 



m 



Fig. 8e. 



Astrangia solitaria.— The development of the mesenteries within the ventral exocoelic chambers is exceptional in that it is in 

 advance of that in the right middle exocoele (rf, fig. 47, PI. VI). 



In tig. 8/', from another polyp, a third-cycle pair occurs in each of the six primary systems. 



m 



ur 



n H 



Fig. 8/. 



A.<tmti:<ia sutitfu-i't. — A pair of second-cycle metacnemes now occurs within each primary exoccele. 



