94 Proceedings of the Royal Physical Society. 



forata ; in Heliopora and its allies, among the Alcyonaria ; 

 in the great majority of the Rugosa ; in Millepora and its 

 allies, among the Hyclrozoa ; and, lastly, in a few extinct 

 types of the Polyzoa {e.g. Radiopora and Heterodictyct). The 

 mere fact of the occurrence of " tabulae " in so many forms 

 of such diverse zoological affinities, is sufficient proof that 

 these structures cannot be used in framing a classification of 

 the corals; but it is at the same time conclusive that the 

 " tabula3 " of these different types, though undistinguishable 

 in appearance, and performing identical functions, cannot be 

 precisely and in all cases homologous structures. As to the 

 " tabulae " in the true Actinozoa, Professor Verrill is doubtless 

 right in believing that they are partitions formed after each 

 discharge of the ova, the vacuity thus formed being useless, 

 and being therefore cut off by a " tabula " from the visceral 

 cavity above. Upon this view, the " tabulae " of the Actinozoa 

 are essentially of the same nature as the " dissepiments " of 

 most of the Zoantharia, only they are formed after the simul- 

 taneous evacuation of all the ovaries at successive periods ; 

 whereas the latter are produced after the successive discharge 

 of the different ovaries, in the different intermesenteric 

 chambers, at diff'erent times. How far, however, there is really 

 an identity in structure and origin between the "tabulae" 

 and the " interseptal dissepiments " is a question into which 

 I cannot enter here. If, however, the "tabulae" of the 

 Actinozoa are periodic partitions formed after the discharge 

 of the ova, then it is clear that they cannot be homologous 

 with the apparently similar structures found in certain sec- 

 tions of the old group of the " Tabulata." Thus, Mr Moseley 

 has shown that the Milleporidce are undoubted Hydrozoa, and 

 that their ova are therefore not produced within the visceral 

 chamber at all. It is consequently clear that in this family 

 the "tabulae" cannot be partitions produced subsequent to 

 the extrusion of the ova. It must also be admitted that any 

 transverse partitions which may be found to intersect the 

 cells of undoubted Polyzoa (such as Heterodictya, Nich.) must 

 be fundamentally different in their nature from the " tabulas " 

 of either the "tabulate" ^ci5mo2;o(X or of the Milleporidce, though 

 they may not be distinguishable from these in appearance. 



