GENERAL REMARKS, 15 
supported by the directive mesenteries, and the interval between these by four mesenteries on 
each side. The directive msenteries and one mesentery on each side (nos. 4 and 9 of 
Fowler’s figure 8)—which, as in Antipatharia, may be termed the transverse mesenteries and 
are the first to be developed—are more important than the others and extend to a lower level. 
The transverse mesenteries are the longest, and are the only ones which bear reproductive 
organs. Similar elongate mesenteries occur in Alcyonaria, in Antipatharia, and in Seriatopora 
and Pocillifera amongst the Madreporaria. In Antipatharia, as in Madrepora, they are 
the only ones which bear reproductive organs. The free extremities of the longer mesenteries 
bear a trilobate mesenterial filament. The retractor muscles of the mesenteries are arranged 
on the hexactinian plan—that is to say, they occur on the outer surfaces of the directive 
mesenteries and on the inner surfaces of all the other so-called pairs. If we use Fowler’s 
terminology, the primary septa are entoccelic in position, and the secondary cycle exoccelic. 
I have elsewhere * suggested the use of the term amphiccelic for bilateral types, and that 
term is probably preferable in this case. If the primary septasare prominent, each septum 
causes a fold to be formed in the wall of the stomodeum in which its distal extremity is 
lodged. Presumably in cases where the directive septa or all the primary septa meet in 
the middle line and become fused together, the stomodeum may be divided into com- 
partments. With the development of a septum the members of a so-called pair of mesenteries 
become pushed further apart, so that in transverse sections of decalcified specimens which 
possess no well-developed septa of the second cycle the entocceles are very broad and the 
exocceles narrow. 
The case of dimorphism is recorded by Fowler to occur in M. durvillei. I have stated 
elsewhere my reason for believing that the species is a variety of M. tubigera. In any case it 
is identical with the fragments recorded by Quelch in the ‘ Challenger’ Reef Corals under the 
name M. capillaris, Klunz. In the species in question there are two types of polyps, both of 
which appear to be irregularly distributed. The one type is quite normal in structure, but 
the other (type A of Fowler) has six of the mesenteries (viz. the axial directives and alternate 
septa afterwards) much thickened. These septa (nos. 2, 4, 6, 7, 9, and 11 of Fowler’s fig. 8) 
bear a tube lined by epiblast, which forms a U-shaped canal opening at both ends into the 
stomodeum. Such polyps are charged with symbiotic alge. This type of polyp appears 
more digestive than the normal one ; but both are also reproductive, although the specialized 
type bears very few ova. 
CLASSIFICATION. 
The classification of the species of Madreporu proposed by Dana is based primarily on 
habit, whilst the form and condition of the radial corallites afford the necessary characters 
for further subdivision. Seven principal divisions are enumerated, with the following 
characters :— 
* “ Notes on the Affinities of the Genus Madrepora,” Proc. Linn, Soc, Lond., Zool. 1893. 
