462 



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 onh" one pair of mesenteries, while the right ventral has two. 



m 



in 



Fig. 8e. 



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



advance of that in the right middle exoeoele (c/, fig. 47, PI. VII. 



In tig. 8/j from another polyp, a third-cycle pair occurs in each of the six i^rimary systems. 



m 



nr 



n n 



m 



Fig. S/. 

 Astraiifjia svUtaria. — A pair c»f second-cycle metacnemes now occurs within each primary exoeoele. 



