MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



4G7 



pair C. C. In the polyp from which fig. lOd was taken a pair of complete mesenteries occurs, 

 in place of the unpaired member of the previous polyp. Below the stomodseal region, the mem- 

 bers i»t' pair I>. I> arc found to belong to the smaller series, corresponding in size with pair B, B. 



Fig. IOo. 



Poriies. — Fig. 10. Increase of mesenteries beyond the protocnemic stage, as exhibited by various polyps. The six pairs numbered I-VI and 

 represented by thicker lin.-* arc the protoenemes. a, An additional bilateral complete pair ( A. At occurs within the exocoele of the 

 ventral pair of directives. 



All the additions thus far are within the entocoele of the ventral pair of directives, but in 

 fig. 11 the new mesenteries are disposed within the entocoele of the dorsal directives. In 11«, 



Fig. 106. 



Poritrs— Two further bilateral pairs have been added; one IB, Bi incomplete, and another (C, C) complete. Mesenteries III, A, on each, 

 side form unilateral isocnemic pair*, in which the retractor muscles are "ii tin- faces of tic- mesenteries turned away from each other, 

 as in directives; mesenteries B, C, on each side constitute unilateral anisocnemic pairs. 



three bilateral pairs are represented, all the members of which are attached to the stomodaeum. 

 The retractor muscles are so disposed that, as in the previous instances, the members of the first 



