396 Dr. J. E. Diicrdeii on the lielationshlps 



stagt'S ill the clevelopnu-nt of Actinian larviB as jjiescutcd by 

 Lacaze-Duthiers in 1873. In doing so, however, he assumes 

 septal and mesenterial relationships differiiifr from any yet 

 eslablished in Zoantharian morphology. 



Uiagi'aiumatic rejMesentation of the mesenteries in a macrotvpic Zoantliid. 

 Five pair^i of primary mesenteries, represented by thicker lines, oecur 

 at the dorsal aspect of the polyp, while the jair of snk-ar directives 

 is ventral. New mesenteries, represented by fainter lines (A-E). are 

 added in succe-sion within the exocoelic chamber on each side of the 

 ventral directives, the oldest (A) being next the dorsal group of 

 primary mesenteries. It will thus be seen that in the living Zoan- 

 thids new mesenteries are successively added at only one exocoelic 

 re^riou on each side of the polyp, while in Lophophyllum they were 

 added at two regions on each side. The entoccelic chamber of the 

 incomplete dorsal pair of directives in the Zoanthids will correspond 

 with the large chief septum of Lfnthuphi/Hum, and the entoccele (f 

 the complete ventral pair of directives, encUising the siphonoglyph or 

 gonidial groove, will corre pond with the small counter septum and 

 st-ptal fossula of LQ2)hophyllum. 



The most recent studies of the Actiniaria and Madreporaria 

 tend to establish a wide division between ordinary anemones 

 and corals, with a cyclical arrangement of the mesenteries, 

 and the Zoanthids and Cerianthids, with a strongly bilateral 

 symmetry. The separation is really founded upon the mode 

 of origin of the metacnemes in the three groujjs, adult sym- 

 metry in the Zoantharia counting for little compared with 

 developmental history. 'J he tendency is to regard each of 

 the three groups as lanking in importance with any of the 

 other great divisions of the Anthozoa, such as the Alcyonaria 

 and Antipatharia. Considerations along sucii lines have 

 induced van Beneden (1897) to remove the Cerianthese alto- 

 gether from their usual association with the Actinians, to 

 make of them an order Ceriantharia, and to place them along 

 with the Antipathaiia under a single division, Ceiiantipathaiia. 



