444 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



in the Alcvonaria and Zoanthida'. If the sulcar a^spect in ail Anthozoa except t'triaiithutf lje 

 conceived as ventral, tlien 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 the general 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 couij)ared: 



Hexactinife, Zoanthea', Madreporaria Sulcar =ventral=posterior. 



Sulc'ular=dorsal =anterior. 

 Ceriantheif Sulcar =dorsal =anterior. 



Sulcular=ventral=poi?terior. 



Where coral polyps present a definite i-elationshij) to the axis of a branch, as in most species 

 of Madrepora^ Ociilina. and Cludocora, axial and abaxial positions are further determinable; and 

 in the rounded colonies of OrhtceUa, Solenmtrma, etc., inner and outer relationships, which 

 correspond with axial and abaxial, are also disting'uishal)le. 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 Madrejxira to the axis of the 

 colony may be first determined. The transverse section on PI. I. tig. 4, 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 pi'oportional 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 al)axial or outer aspect 

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

 The large anterior tentacle of Madrepom thus communicates with the sulcular, and the posterior 

 tentacle with the sulcar entoctele. 



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 Mudrcpom are reversed. Thus on PI. VIII, tig. (U, repres(Miting a l)ud of CUidoeoro w\\\\ the 

 protocnemes in the Edwirdfii'ti-t^ta.^e, the sulcar aspect of the polyp is al)axial or outward, and the 

 sulcular is axial or inwards, in relation to the colony; similarly in fig. 62, representing another 

 bud of the same species. In fig. ST, PI. XII, taken from a young l)ud of SoJenastrifa, the sulcar 

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



Dr. G. H. Fowler (1SS7), in his studies of Madrepom durvillei and M. mpera, was the first to 

 determine the axial-abaxial relationsiiips 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 Scradvjjora sidjulata^ 

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

 pora and other corals can best be appreciated by comparing the diagrams on page 4-15. 



Dr. Carlg-ren (1890) has shown that in colonial Zoanthida' the macro-directive mesenteries and 

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

 polyp, while the micro-directive mesenteries and asulcular extremity of the stomoda'um 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 therefoi'e in strict conformitj' with that in Madreporaria, the genus Mitdrcpora excepted. 



The researches of Mo.seley, Hickson, 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> of Actiniaria and ^ladreporaria as a resting stage for a long period. Among 

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



