464 MEMOIRS OF THE NATIONAL ACADEIMY OF SCIENCES. 



Fig. 9/t represents a transverse section throiiuh a polyp of P. innertcdiKi. in whicli ten pairs 

 of mesenteries are eompletc; six pairs represent the protocnemes, while the other four pairs 

 belono- to the second order. The remaining two pairs of secondaries are still incomplete. The 

 full complement of twelve tertiary pairs is present, except for one pair in the dorsal exoccele of 

 the two ventral primary systems. Here, as before, it will l)c understood that the dorsal and 

 ventral aspects wer(> not actually deterniiiia)>lc. 



Fig. it/, from a still largt'r polyp of Plnjlhuujin. reveals twelve pairs of complete mesenteries 

 belongiiu'- to the first and second orders, and twelve alternating pairs of incomplete mesenteries 

 representing the third order. At the dorsal extremity a few pairs of mesenteries of the fourth 

 order liave also appeared. Polyps of Phijlhuui'ia rarely contain more than this number of 

 mesenteries, so that it has not been possible to follow tiie method of growth of the fourth 

 order. All that can be asserted from tig. 9/ is that the mesenteries of the fourth order begin to 



Fig. 971. 



Phyllanrjia omerimna.— Order of appearance of the metacncmes continued. Other pairs of second-cyele metacncmes (III) are present, and 

 four pairs of the first-cycle metacnemes (11) are now united with the stomodteum. The succession of growth is from the dorsal to the 

 ventral aspect. . 



make their appearance at one extremity of the polyp, which is pii>b;d)ly the same as that at which 

 the members of the second and third orders first arise. 



The sections of the polyps of Far in frag am represented on page 51t>, and of Manicina areolatn 

 on page 504, reveal that in the.se .species the order of appearance of the third-cycle mesenteries 

 follows a succession closely comparable with that in Clad^cora. Asfni/ir/ni, and Phylhnigia. 



The order in which the twche pairs of tertiary mesenteries are developed may be thus 

 summarized: 



The members of the third order of mesenteries arise in successive isocnemic pairs, after 

 the establishment of the secondarj' mesenteries, within the exoctelic chambers between the 

 pairs of the first and second orders of mesenteries. In a general way, two stages of growth are 

 distinguishable: First, a single pair arises within each of the six primary .systems, that is, within 

 onlj' one of the two exocceles, the succession being from one aspect of the polyp to the 



