302 MR- J. E. DUERDEN OK 



armed stage passed through by most Scyphostoma, and the 

 arrangemsBt of the four canals, with the circumferential sinus 

 terminating in eight divisions bifurcated at the end, resembles 

 a gastro-vascular system such as that of the Ephyra. 



Though in the particular case of Lehrunia the eight tentacles 

 develop simultaneously, it does not follow that they may not 

 have had an ancestry in which they arose in pairs, as happens in 

 the Scyphostoma. Por there is evidence that such fundamental 

 structures as the primary mesenteries develop successively in 

 pairs, as is the case in all other Zoantharia. The two consti- 

 tuting the fourth pair (sulcular directives) in most cases disappear 

 at the aboral end before the others, and in every case the first 

 pair (suleo-lateral) are larger than the others, and are the only 

 ones which bear mesenterial filaments. 



The results appear to justify to a greater degree than has 

 before been possible Hseckel's and Gotte's union of the Scypho- 

 medusse and Actinozoa under the term Tseniolatse or Scyphozoa ; 

 a relationship first rendered probable by the discovery of the 

 ectodermal character of the stomodaeal lining of the former, and 

 the presence of mesenteries and gastric filaments. The strong 

 objection founded on the tetrameral character of the Scypho- 

 medusse, as compared with the hexameral nature of tlie Acti- 

 niaria, disappears on the demonstration that the larvge of the 

 latter may pass through a tetrameral stage, directly comparable 

 with that permanent in the former. 



Further, where the transition from one stage to the other can 

 be iollowed in the ontogeny of a single form, we have another 

 to the many objections agaicstthe separation of the Tetracorallia 

 or Rugosa from the Hexacorallia. There can be no fundamental 

 distinction on the ground of symmetry alone. 



The very marked arrest of the mesenterial and tentacular 

 development in Lehrunia at a tetrameral or octameral stage, and 

 the fact that such occurs to a greater or less degree in apparently 

 all other Zoantliaria {Ldivard sia-st&ge), suggest this as either a 

 permanent stage or as a starting-point for various modifications, 

 and emphasizes with how little reliability adult structure can be 

 accepted as evidence of phylogenetic relationship. 



The E.ugosa and Alcyonaria retain approximately a tetrameral 

 or octameral type of symmetry, while the Hexacorallia and 

 Actiniaria, by the further addition of two lateral pairs of 



