ANATOMY OF MUSSA AND EUPHYLLIA. 33 



corals based on a study of the corallum alone is unsatisfactory, 

 and that any attempt to remodel the old classifications should 

 depend on a systematic study of the relations between the 

 corallum and the polyp. Owing to the difficulty of obtaining 

 material, and of dealing with it when obtained, the number 

 of forms examined is as yet small, and the results of recent 

 researches have not advanced us very far towards an improved 

 classification. The most recent attempt to remodel the 

 systematic treatment of the group is Professor Martin Duncan's 

 " Revision of the Families and Genera of the Madreporaria," 

 'Linn. Soc. Journ./ xviii, in which the older classifications 

 are amended in some important particulars, several old families 

 have been struck out or merged with other families, and the 

 Fungidse are raised to the rank of a group equal in value to 

 the Perforata and Aporosa. But whilst all the definitions, by 

 far the greater part of the classification, depend on the old 

 distinctions in the characters of the corallum, scarcely any 

 weight is given to the development and anatomy of the polyp. 

 Although but little has been done even in working out the 

 anatomy of adult forms, and although our knowledge of the 

 development of the Madreporaria is miserably insufficient, we 

 have sufficient information about the group to enable us to 

 make certain generalizations about it. 



The pricipal workers on Madreporaria have been de Lacaze 

 Duthiers, Moseley, G. von Koch, von Heider, and Fowler, 

 whose separate memoirs are referred to in the course of this 

 paper. In all, the anatomy of some twenty forms has been 

 worked out more or less completely, and the development of 

 one species, Astroides calycularis, has been followed by 

 two observers, H. de Lacaze Duthiers (' Arch, de Zool. exper. 

 et. gen./ ii, 1873, p. 269), and G. von Koch (< Mitth. der Zool. 

 Stat./ Neapel, 1882). 



Anatomy of the Polyp. — In the majority of the forms 

 examined the structure of the polyp, both in grosser anatomy 

 and in histology, is essentially that of an Actinia. The mesen- 

 teries are arranged in pairs, and frequently if not usually in 

 cycles of six pairs each. But recent observations have shown 



VOL. XXVIII, PART 1. NEW SER. C 



