68 me. Stanley smith on [March 19 13, 



(3) Independence of Variations in the Different Parts of 

 the Corallum. 



Each detail, as has just been shown, of coral structure is 

 subject to considerable variation. These details vary indepen- 

 dently of one another, except in so far as the development of one 

 actually controls the other : as, for example, the influence of the 

 septal lamellae upon the central vesicles. The diameter of the 

 central column, the intensity of its structure, the design presented 

 by the septal lamellae, the width of the space free from septa 

 around the central column, and the width of the area occupied by 

 the tabular vesicles and the dissepimental zone, all vary without 

 any obvious connexion with each other. The result is an endless 

 series of slightly different variations of the same general plan. 



(4) Intensity l and Design of the Central Column considered 

 with a view to Classification. 



The central column is the most conspicuous and at the same 

 time most variable feature of the coral, and it was mainly upon its- 

 horizontal aspect that Thomson founded his various species. 



The tissue of the column (especially the septal lamellae) affords 

 wide scope for differentiation, as regards both intensity and design : 

 and these two distinct lines of variation must be considered before 

 we attempt a classification. 



Intensity can have both a phylogenetic and an ontogenetic signi- 

 ficance, and is of much more importance than the design. The 

 adult forms from the lower part of the Dibunophyllum Zone (D t ) 

 6how an intensity parallel to that developed at Stage D in forms 

 from the higher portion of the zone, D„ and D 3 . Forms are 

 found together, in the higher horizon, which range in intensity 

 from a stage little advanced from Stage D to the most advanced 

 types of Stage F. This indicates failure on the part of the 

 less specialized individuals to attain the maximum of possible 

 development. 



The design is an individual character ; and, although the 

 prevalence of a particular type often characterizes the Aidophylla 

 from a certain locality or from a particular bed, forms expressing 

 the different types are found side by side. The well-marked and 

 recognizable types are but the extremes of variations in the several 

 directions. 



That development of the intensity and design of the central 

 tissue is not merely a matter of time or environment, but depends 

 also on other and unknown factors, is emphasized by the fact that 

 marked variation in these characters may be seen in adjacent 

 corallites of Lonsdalia (citing this genus merely by way of 

 example). Mr. F. Wood-Jones draws particular attention to the 

 enormous range of variation in the skeletons of living coral-genera 

 existing under very slightly different conditions. 2 



1 Intensity is bere used to indicate ' crowded condition ' of the tissue. 



2 ' Corals & Atolls ' chapt. viii, 1910. 



