C2 ME. STANLEY SMITH ON [March 1913, 



The insertion of septa ceased when the corallum reached the 

 cylindrical stage, and the last-formed septa having attained the 

 same size as the others, the pinnate aspect was superseded by a 

 bilateral, or even radial symmetry. AulopJiyllum with other forms 

 assumed a bilateral symmetry, in virtue of the shortened cardinal 

 septum, which kept open the cardinal fossula. In those forms 

 in which the cardinal septum was not conspicuously shortened 

 the radial symmetry replaced the pinnate. 



In PI. V, fig. 1, the septa are seen to unite and coalesce in the 

 centre of the corallum, but at a very early stage they became free ; 

 in PI. V, fig. 2, this process is just commencing. 



(b) Minor septa. — The first minor septa to appear in the 

 coral were inserted between the already existing major septa, 

 at a point situated a short distance from the proximal end of the 

 corallum. The subsequent members were introduced at the fossula) 

 or after the last-formed major septa had developed : that is, 

 between 5 c and 4 c, and between 6 a and 5 a. 



(c) Septal lamellae. — In a section through the very young- 

 portion of the coral, the major septa penetrate the wall of the 

 central column, and are prolonged within it as thin flexuous 

 lamellae (PI. V, fig. 3). The septa retreated, however, as develop- 

 ment progressed, and (PL V, fig. 4) eventually left a clear annular 

 space between their ends and the central column (PI. V, fig. 5 a). 

 The thin lamellae thus either became free, or remained connected to 

 the ends of the septa as before (PI. V, fig. 4) ; but later most, if 

 not all, became separate (PI. V, fig. 5 a). Simultaneously with 

 this development, fresh lamellae grew out from the ' wall ' of the 

 central column between the existing lamellae of direct septal 

 origin : hence the number of septal lamellae greatly exceeds that of 

 the septa. 



In the earliest stages, the septal lamellae merely fringe the inner 

 wall of the central column (PI. V, figs. 3 & 4) ; but certain of 

 their number soon advanced into the vesicular tissue, and the rest 

 converged with these longer ones (PI. V, figs. 5 a-5 c). The 

 character of the septal lamellae, as shoAvn elsewhere (p. 67), is 

 very variable, and their development is irregular ; but generally a 

 radial arrangement, in which the lamellae are fairly straight and 

 not in a crowded condition (PI. V, figs. 5 h & 7 «), precedes a 

 more irregular plan of compacted lamellae (PI. V, figs. 5 c & 7 b). 



(cl) Columnar and tabular vesicles. — One class of vesicles 

 only — simple vesicles of a tabular character were formed near the 

 proximal end of the corallum. These were followed by others, 

 arched in the centre and bent backward towards the margin. 

 The succeeding vesicles broke up into arched tabulae and tabular 



