STRUCTURE AND RELATIONS OE CERTAIN CORALS. 
121 
the octameral arrangement of the mesenteries, a hexameral disposition, in being often 
twelve in number, it seems that the question of the affinities of the Eugosa may fairly 
be reopened. The presence of well-marked calcareous septa in Cryptohelia and other 
Stylasteridse (which septa are equal to the tentacles in number, but nevertheless to be 
regarded, like those of Meliopora, as pseudo-septa) is significant. The marked tetra- 
meral arrangement of the septa in Eugosa, and the presence in many forms of tabulae, 
are certainly characters not opposed to the alliance of these corals with the Alcyona- 
rians ; and the fact that paired series of opercula occur in certain Eugosa, which are 
compared by Lindstrom, their discoverer, to the skeletal structures of certain Primnoce , 
seems to be evidence in favour of such an alliance of the very strongest kind. In no 
Madreporaria do paired hard structures, at all resembling those of Primnoce or of 
Goniophyllum pyramidale, occur. The opercular structures in the coralla of Cryptohelia 
and Lepidopora can scarcely be regarded as comparable with the opercula of Eugosa. 
The structures are merely folds of the lip of the calicle, and are continuous with it and 
immovable, not movable separate articulate structures. Many Eugosa show an arrange- 
ment which may well be compared to the distinction of dorsal and ventral regions in 
Alcyonaria. The most important distinctive character of the Eugosa appears to be the 
occurrence in them, alone of all Anthozoa, of intracalicinal gemmation *. 
With regard to Sarcophyton, the fact that compound colonies composed of multitudes 
of zooids, combined with a lesser number of sexual polyps, occur amongst the Alcy- 
onidee, as well as amongst the Pennatulidse, in which they are so well known from 
Kolliker’s great work, appears to be new to science. That in such colonies and in 
Heliopora the “Dorsalfacher” are all turned towards the axis of the colony and directed 
upwards is also a new fact. The zooids in their structure seem to conform very closely 
to those of Pennatulids ( Sarcophyllum , e. g.) ; but to the list of distinctive differences 
between the zooids and polyps of Pennatulids given by Kolliker, viz. the absence in 
the zooids of tentacles, the presence of two mesenterial filaments (the dorsal ones), the 
absence of generative organs, and the shortening of the hypogastric region to such an 
extent that it fuses with the anastomosing canal-system — to these marks of distinction 
must be added, in the case of the zooids of Sarcophyton , the fact that four of the 
mesenteries, the dorsal and ventral pairs, are deeper than the others. 
It seems extremely difficult to reconicle the extraordinary succession of the mesen- 
teries in the development of the Zoantharians, discovered by Lacaze-Duthiers, with the 
facts presented by Alcyonarians. Did the development of the eight mesenteries of Alcyo- 
naria correspond with that of the first eight mesenteries formed in Actiniadae, the first 
mesenteries formed would be either the lateral dorsal or lateral ventral; but these are 
those which are most rudimentary in the zooids of Sarcophyton. Moreover the mesen- 
terial filaments of the two lateral pairs of septa are in the development of Actiniadae 
the first to appear, and not the dorsal, which are longest in the Alcyonarian polyps and 
* An examination of tlie Comulariadse, the only recent solitary Alcyonarians, might very possibly throw 
light on the question of the affinities of the Rugosa. 
