MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



407 



pair C, C. In the polyp from which fig-. li)(l was talten a pair of (-omplete mesenteries occurs, 

 in place of the unpaired member of the previous polyp. Below the stomoda?al reg'ion, the mem- 

 bers of pair D, D are found to belong to the smaller series, corresponding in size with pair B, B. 



Fig. 10a. 



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

 represented by thicker lines are the protocnemes. a. An arlditional bilateral complete pair(.\. A) occurs within the exoccele of the 

 ventral pair of directives. 



All the additions thus far arc within the entoccele of the ventral pair of directives, but in 

 fig. 11 the new mesenteries are disposed within the entocosle of the dorsal directives. In lla, 



Fib. 106. 



Poritca. — Two further bilateral pairs have been added; one (B, B) incomplete, an'l another (C, C) complete. Mesenteries III. A, on each, 

 side form unilateral isocnemic pairs, in which the retractor muscles are on the faces of the 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 tlie members of which are attached to the stomodteum. 

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



