AFFINITIES OF THE GEXUS MA.DEEPOEA. 355 



In transverse section " concentric circles of thin calcareous 

 structure are seeu, separated by radiating linear pillars ; the 

 circles having been in turu outside wall and the radii either 

 spinules or costae." If the coral is old the inner circles of tissue 

 next the septal cavity are dense. Duncan also pointed out that 

 no communication exists between the cavities of bud and axial 

 corallites " except in a very indirect manner and through the 



medium of the dermal structures Budding takes place 



remote from the calicular margin and may arise from scleren- 

 chyma remote from the wall of a corallite." Thus the density of 

 the corallite depends to a great extent on the breadth of the so- 

 called costae a.nd is always densest where the costse are replaced by 

 fine echinulations. 



A further point remains to be noticed which appears to me 

 important. As a result of the peculiar mode of budding in the 

 genus Madrepora — which leads to the formation of a type of colony 

 termed " patrioramose " by Dana — there is no coenenchyma in the 

 true sense of the word excepting at points where the colony is 

 incrusting. The radial corallites are arranged on the branches at 

 variable intervals, and the space between them is usually con- 

 sidered to consist of ecenenchyma; but these intervals really form 

 part of the thickened wall of the axial corallite around whicb the 

 radial corallites are developed, and the trabecular network of 

 which they are composed is not precisely comparable with the 

 interzooidal ecenenchyma of Turhinaria, for example, which is a 

 true secretion of interzooidal tissue and not of the walls of the 

 zooids themselves. 



The skeletal structure of the genera Anacropora, Montipora, 

 Porites, and Turhinaria has hitherto received little attention. 

 I have not as yet made a complete study of the question ; the 

 following notes are based on the study of only one or two species 

 in each genus and, though sufficient for my present purpose, may 

 need revision later. In Anacropora and branching species of 

 Montipora the axis of a brancb is occupied by elongate fibrous 

 trabeculge similar to those which constitute the trabecular type 

 of columella in most genera of Madreporaria. Around this axial 

 mass a network of shorter processes occurs in which the coral- 

 lites are embedded ; the intervals between the corallites consist 

 of true coenenchyma. The mode of budding is intercalicular but 

 apparently the individual corallites remain directly connected 

 together ; in any case the stolon-like canals by which they are 



