456 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



no instance did they stretch wholly across, and become united with the stomodseum. Subsequent 

 examination, by means of sections, showed that in each pair the retractor muscles were disposed 

 on the faces turned toward each other, thus resembling the unilateral pairs of the first cycle. 



£ 



Fig. «. 



Sideraatrsea radians.— Three diagrammatic figures illustrating the order of appearance of the first cycle of metacnemes in larval polyps. 



The Roman numerals I arc opposite the protocnemic fairs, and the letters A.-C indicate the succession of the metacnemes. 



While the actual mode of appearance of the mesenteries could be thus followed step by step in 

 Sta< rastrsea, young polyps of Faviafragum were obtained with the mesenterial conditions shown 

 on pp. 509, 510, and from these certain conclusions are warranted. Four pairs of second-cycle mes- 

 enteries are present in fig. 15, , i n addition to the six pairs of protocnemes. Of the four metacnemic 



