444 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



in the Alcyonaria and Zoanthidse. If the sulcar aspect in all Anthozoa except Oerianthus be 

 conceived as ventral, then in the latter it will be dorsal as well as anterior, and the ventral or 

 sulcar aspect in other Anthozoa is posterior. It is shown later that thegeneral succession of growth 

 of the mesenteries in Madreporaria is also from the dorsal to the ventral aspect of the polyp, that 

 is. they arise in an antero-posterior order. The septa have also been found to follow a like suc- 

 cession. 



The relationships may be thus compared: 



Hexactinise, Zoanthese, Madreporaria Sulcar =ventral=posterior. 



Sulcular =dorsal =anterior. 

 Cerianthea' Sulcar =dorsal =anterior. 



Kulcular=ventral=posterior. 



Where coral polyps present a definite relationship to the axis of a branch, as in most species 

 of Madrepora, OcuUna, and Cladocora, axial and abaxial positions are further determinable; and 

 in the rounded colonies of Orbicella, Solenastrsea, etc.. inner and outer relationships, which 

 correspond with axial and abaxial, ai - e also distinguishable. Some importance underlies these 

 determinations, for it will be found that the axial-abaxial and sulcar-sulcular relations are not 

 always the same in corals. 



The relationships of the strongly bilateral, radial polyps of Madrepora to the axis of the 

 colon}' may be first determined. The transverse section on PI. I, fig. -I, represents the polyp as 

 situated in relation to the axis of the branch, but the lower side in the figure is inner or next the 

 axis, and the upper is outer or turned away from the axis. Owing to the nariform growth of the 

 corallite the skeletal tissue is more thickly developed on the upper than on the lower aspect. 

 From the proportional development of the mesenteries, and the disposition of the longitudinal 

 musculature, it is clear that the axial or inner aspect is the sulcar, and the abaxial or outer aspect 

 the sulcular: or, in the terminology usually adopted, the former is ventral and the latter dorsal. 

 The large anterior tentacle of Madrepora thus communicates with the sulcular. and the posterior 

 tentacle with the sulcar entocoele. 



Wherever in other corals it has been possible to determine the sulcar-sulcular relationships, 

 as well as the axial-abaxial, to the colony as a whole, it is found that the relationships prevailing 

 in Madrepora are reversed. Thus on PI. VIII, fig. 61, representing a bud of Cladocora with the 

 protocnemes in the Edwardsia-stiLge, the sulcar aspect of the polyp is abaxial or outward, and the 

 sulcular is axial or inwards, in relation to the colony; similarly in tig. ti'2, representing another 

 bud of the same species. In tig. 87, PI. XII, taken from a young bud of Solenastrsea, the sulcar 

 side of the polyp is again outward (abaxial) and the sulcular is inward (axial). 



Dr. G. H. Fowler (1887). in his studies of Madrepora durvillei and M. aspera, was the first to 

 determine the axial-abaxial relationships of the mesenteries in the genus, and the year following 

 (1888, p. 12) he showed that it was directly the opposite of that occurring in St riatopora svbulata, 

 the polyps of which also permit of axial-abaxial determinations. The difference between Madr, 

 pora and other corals can best be appreciated by comparing the diagrams on page 115. 



Dr. Carlgren (189<i) has shown that in colonial Zoanthidse the macro-directive mesenteries and 

 the single gonidial groove are on the outermost side of the colony, or farthest from the mother 

 polyp, while the micro-directive mesenteries and asulcular extremity of the stomodseum are 

 toward the inner side of the colony, or nearest the parent polyp; the anterior (dorsal, asulcar) 

 part is directed toward the axis of the colony, while the posterior (ventral or sulcar) is 

 turned away from it (fig. c). The relationship of the individual polyp to the Zoanthid colony 

 is therefore in strict conformity with that in Madreporaria, the genus Madrepora excepted. 



The researches of Moseley, llickson, and others on the Alcyonaria have also demonstrated 

 that in this group the relationship of the polyp to the axis is the same as that in most Madre- 

 poraria. The so-called ventral aspect (sulcar) of the Alcyonaria is abaxial. the dorsal aspect 

 (asulcar) is axial (tig. d). 



The stage of mesenterial development with only four pairs of complete mesenteries usually 

 serves the larva 1 of Actiniaria and Madreporaria as a resting stage for a long period. Among 

 the Actiniaria the only forms known in which the adult was thought to remain at this simple 



