ANATOMY OP MUSSA AND ETJPHYLLIA. 49 



theca of Flabellum as epitheca, much as I disagree with many 

 of his expressed views on epithecal structures. 



The only arrangement, then, which our present knowledge of 

 the Madreporaria permits us to make, is as follows : 



1. Madreporaria with no directive mesenteries and a per- 

 fectly radial symmetry, Lophohelia, Mussa, Euphyllia. 



2. Madreporaria with directive mesenteries and a combined 

 radial and bilateral symmetry, Turbinaria, Rhodopsammia, 

 Fungia, and many others. 



3. Madreporaria with reduced radial symmetry and marked 

 bilateral arrangement of parts, Madrepora, Pocillopora, 

 Seriatopora. 



4. Madreporaria with a basal pseudotheca and no " Rand- 

 platte," Flabellum. 



I do not pretend that this arrangement has the value of even 

 an incomplete natural classification, but it is the best arrange- 

 ment that the facts warrant us in making. Finally, it must be 

 observed that the skeleton of the Madreporaria differs widely 

 from that of Alcyonaria. In the former the calcareous tissue 

 is nearly certainly elaborated and secreted by the ectodermic 

 cells ; it is always external to the polyp. In the latter, ecto- 

 dermic cells early separate from their primitive position, be- 

 come embedded in the mesogloea, and develop spicules within 

 their substance. The skeleton then is within the polyp. In 

 some cases skeletal structures may in the latter group be 

 developed within endoderm cells (E. B. Wilson, " The develop- 

 ment of Renilla," "Phil. Trans./' clxxiv, p. 723). 



Unsatisfactory as the conclusions as to classification given 

 above may be, I hope that I have succeeded in presenting the 

 facts known about the morphology of the Madreporaria in a 

 manner comprehensive enough to be of use to future investi- 

 gators in a difficult field. 



VOL. XXVIII, PART 1. NEW SER. 



