REPORT ON THE ACTINIARIA. 



35 



referable chiefly to the fact that the forms described had been quite insufficiently 

 studied, and that consequently the systematic characters had been referred to points of 

 secondary moment only. In this condition of affairs no alteration has been effected by 

 the monograph of Angelo Andres ; the great abundance of forms cannot be compressed, 

 as he has attempted to compress them, into the three genera, Zoanthus, Palythoa, and 

 Sphenopus (the genera Verrillia, Bergia, and Antinedia having but a doubtful position, 

 so long as we possess such scanty information about them as at present). 



I have therefore requested Dr. Erdmann, one of my students in Bonn, to undertake 

 a revision of the Zoantheaj with reference to the following important anatomical 

 characters : — (l) condition of the ccenenchyme ; (2) arrangement of the mesenteries ; (3) 

 structure of the sphincter; (4) condition of the integument; (5) colony - formation. 

 His conclusions are as follows : — The Zoanthese may live solitary (Sphenopidse), or may 

 form colonies (Zoanthidse) ; in the latter case the ccenenchyme may either consist of 

 basal stolons more or less branching, sometimes even anastomosing, or of a connecting 

 lamella, or of a mass which unites the polyps almost for their whole height. The 

 integument either consists merely of an epithelium and cuticle, or else there occur 

 on it foreign bodies, which penetrate the mesoglcea of the body-wall, and more or less 

 fill it. In the arrangement of the mesenteries two points are of importance : (l) that 

 the pairs of mesenteries, with the exception of the directives, consist of a macro- and 

 a micro-mesentery ; (2) that a dorsal and a ventral zone of mesenteries must be 

 distinguished. The two zones may approximate either with small (Microtype) or with 

 large mesenteries (Macrotype). Finally, the sphincter exhibits three modes of forma- 

 tion ; it may be (l) endodermal; (2) mesoglceal ; (3) it may be mesoglceal, but 

 distinguished by a muscle-free region into upper and lower portions. 



AVith reference to the points above mentioned, Erdmann has distinguished five 

 genera in the colonial Zoanthidse, the characteristics of which may be followed without 

 further comment in the accompanying table : — 



