45G 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



IK) instaiuo did they stretch wholly across, and become united with the stomodfeum. Subsequent 

 pxaniination. hy 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. 



B 



Ir. 



Sidtraslra-a mil ians.— Three diagrammatic figures illustrating the order oj appearance o£ the first cycle iif metacnemes in larval polyps. 

 The Roman numerals I are opposite the protoencmic pairs, and the letters A-C indicate the succession of the metacnemes. 



While the actual mode of appeaianc(> of the mesenteries could be thus followed step by step in 

 Siderastrivd, young polyps of Fai'lafraguin were obtained with the mesenterial conditions shown 

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

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



