CLASSIFICATION. ii 



in the ordinary acceptation of this term, though the " tabulae " 

 are well developed. Moreover, it begs the question at issue to 

 speak of the vesicular plates of the Cystiphyllidce as being of the 

 nature of " crowded and regular horizontal dissepiments ^ which 

 simulate " tabulae ; " since it is just as likely that they are 

 crowded and anastomosing tabula;, which simulate " dissepi- 

 ments." In the entire family of the Chcstetidcs (assuming these 

 in the meanwhile to be Actinozod) the "tabulae" are well de- 

 veloped; but there are no septa, and therefore no "dissepi- 

 ments," unless the latter are represented by the tabulae. 

 Lastly, in the HelioporidcE it has been shown by Mr Moseley 

 that the so-called septa are not homologous with the septa of 

 the Zoantharia ; and it is therefore improbable that the well- 

 developed tabulae of the former should be homologous with 

 the " interseptal dissepiments " of the latter. 



Whatever may be, however, the nature of the " tabulae " 

 in the various groups of Actinoza which possess them, and 

 whether or not they are always periodic partitions formed 

 after the discharge of the ova (Verrill), or mere modifications 

 of the interseptal dissepiments (Lindstrom), it is clear that 

 they cannot be homologous with the apparently identical struc- 

 tures in certain other sections of the old group of the " Tabu- 

 lata." Mr Moseley, for example, has shown that the Milleporce 

 are truly Hydrozoa, and that their ova are therefore not pro- 

 duced within the visceral chambers. It is clear, therefore, that 

 in these forms the " tabula; " cannot be modified " dissepi- 

 ments," and still less partitions formed subsequent to the 

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

 transverse plates which may be found to intersect the cells of 

 undoubted Polyzoa (such as Hetei-odidya, Nich.) must be of a 

 fundamentally different nature to the "tabula;" of either the 

 "tabulate" Actinozoa or of the Millepores, though they may 

 not be distinguishable from these in appearance, i 



1 It follows from the above that if the name of " tabulas" be retained for tlie 

 transverse partitions found in the visceral chamber of certain Actinozoa, it can 

 hardly be said in any strict scientific sense that " tabula:" are present in certam 

 Hydro-oa {Milkporida) and certain Polyzoa {Hctcrodidy.i). The proper course, 



