ANEMONES 375 



SYSTEMATIC ACCOUNT. 



Order ACTINIARIA. 



Ccelenterata with mesenteries usually numerous and in some multiple 

 of six ; without spicular or continuous skeleton. Polyps either free, or 

 adhering by means of pedal disk, or, rarely, fixed ; for the most part 

 solitary, occasionally forming colonies. 



Tribe HEXACTINIyE Hertwig. 

 Actiniaria with at least eight perfect mesenteries which correspond 

 to the first eight mesenteries of the embryo ; with a varying number 

 of secondary mesenteries, four of which form, with the primaries, six 

 more or less complete pairs ; these constitute the first cycle, which may 

 be augmented by two or four pairs of perfect mesenteries. To this 

 first cycle may be added a number of additional cycles, perfect or im- 

 perfect, the mesenteries of which usually develop in pairs and radially, 

 appearing almost simultaneously in all the intermesenterial spaces. 

 The longitudinal (retractor) muscles of each pair face toward each 

 other except in the case of two (or one or several). The directives, 

 which are usually attached to the siphonoglyphs and whose retractors 

 face away from each other, toward the adjacent intermesenterial spaces. 



Order EDWARDSI^ Hertwig. 



Free-moving non-colonial Actiniaria^ with eight primary perfect 

 and a variable number of secondary rudimentary mesenteries. Of the 

 primary mesenteries, two pairs are directives ; the remaining four are 

 unpaired and their retractor muscles face the same way ; all are fertile. 

 Tentacles simple, never more numerous than the mesenteries. 



This is essentially the definition of Haddon modified to accord with 

 the observations of Faurot and myself concerning the presence of 

 secondary mesenteries in the Edwardsiidie, a fact which will be dis- 

 cussed farther on. 



The reincorporation of the Edwardsiaj into the Hexactinitc has been 

 necessitated— as Van Bcnedcn and McMurrich have already decided 



by the discovery of a true though primitive hexactinian arrangement 



of mesenteries in some species of the former group, e. g., E. beau- 

 tempsi. Whether this condition is primitive in Ed-wardsia or, as 

 Van Beneden holds, has been secondarily produced by the simplifi- 

 cation of a more complex hexactinian ancestor is a question which I 

 do not think we are now in a position to decide. It seems probable, 



