of the Rugosa to the livinj Zuanthea'. 3S9 



end constitute alternatin<r liexamenil cycles; in tlje Zoaii- 

 tliea-, as tlie researclios of von Kocli (18.S0), Eidniann (1885), 

 and many others liave shown, the new mesenteries are deve- 

 loped at only two regions, the exocoele on each side of the 

 ventral directives, and the adult polyps are strongly bilateral 

 (fig. 12); in the perforate corals Forites and Madrepora I 

 have recently found that the mesenteries beyond the six 

 primary pairs appear as bilateral pairs within the directive or 

 axial entocoeles, thus recalling the method of mesenterial 

 growth characteristic of the Cerianthidea after the formation 

 of the first four pairs (1900). 



It remains to be seen how close the septal conditions 

 occurring in Lophophyllum can be brought into relationship 

 with those of modern corals or the mesenterial plan of 

 Actiiiians. The late Prof. H. de Lacaze-Duthiers (1873, 

 1897) and G. von Koch (1882, 1897) have described the 

 primary stages in the formation of the corallum of living 

 species of AstroiJes, Cori/c^/it/llia,&c., and in all cases either 

 six or twelve septa are formed simultaneously ; in the course 

 of the postlarval development of the West- Indian corals 

 Manidna areolata, Favia fragum, and Siderastra-a rjdians I 

 have also found that six septa first appear, arising within the 

 entocoelic chambers of the six primary pairs of mesenteries. 

 Thus the protosepta are hexameral in all the representatives 

 of the three sections of living corals — Aporosa, Fungacea, 

 and Perforata — whose early development has been followed. 



As far as the protoseptal stage, therefore, the hexameral 

 plan of its primary septa at once places the Palasozoic 

 Lophophyllum in agreement with recent Madreporarian 

 corals, and renders unnecessary any attempt to account for a 

 primitive tetramerism. 



It is otherwise, however, with the subsequent stages of 

 development. Very few observations have been made upon 

 the actual manner of appearance of the secondary septa in 

 corals; but in practically all modern species the septa beyond 

 the primary six are fnund disposed within the six interspaces 

 separating the primary members, and ultimately they are 

 radially arranged in regular alternating hexameral cycles, just 

 as are the mesenteries. Certain exceptions to this general plan 

 occur, but do not in any way introduce any distinct funda- 

 mental type, except in the case of the genera Porites and 

 Madrepora, where new septa arise within the axial or direc- 

 tive entocoeles — that is, in the position occupied by the 

 primary axial septa. 



The later septa in Lophophyllum, as in most other Zaphi-en- 

 toid corals, arise bilaterally within only four of the six primary 



