60 



ME. STANLEY SMITH ON 



[March 19 13, 



(iii) An outer cone of smaller and more regular vesicles (the 

 dissepiments proper). These dissepiments are more 

 arched than the tabular vesicles, and their convexity 

 is towards the middle of the corallum. 



The septa are of two orders, major and minor. The major septa 

 extend nearly to the central column, leaving, however, an annular 

 space around it, traversed sporadically only by lamellae joining the 

 ends of the septa with the inner zone. The minor septa usually 

 cross the dissepimental zone, but do not extend far into the area 

 occupied by the tabular vesicles. 



The cardinal fossula is conspicuous ; it is occupied by a short 

 cardinal septum, and in the young and adolescent stages by two 

 developing septa. Alar fossula? are seen only in the immature 

 stages, and are situated between 80° and 90° from the cardinal 

 fossula, shown well in PI. V, fig. 7 a. 



V. Ontogenesis. 



First the origin and growth of the component parts of the 

 corallum will be described in detail, then will follow a more 

 cursory survey of the development of the corallum considered as 

 a whole. 



Origin and Growth of the Component Parts of 

 the Corallum. 



(«) Major septa. 



Fig. 2.— (After 

 Garruthers.) 



C-K=Axial septum. 

 C = cardinal septum. 

 A = alar septa. 

 K = counter-septum. 

 L = counter-lateral septa. 



-Mr. Pi. G. Garruthers 1 has shown that the 

 primary septal plan of the Pugosa is hex- 

 amerous, as in the case of the Aporosa ; 

 but, unlike the newer Zoantharians, which 

 form their six primary septa simulta- 

 neously, the nepionic Pugosa first laid a 

 single septum extending across the coral- 

 lum (the axial septum), which subsequently 

 broke in two to form the cardinal and 

 counter-septa. From the axial septum 

 sprang two pairs of septa, the alar and 

 counter-lateral. 



The first four secondary septa then 

 appeared (1 a, 1 a', 1 c, & 1 c) in the 

 position indicated in the diagram (fig. 3). 



Four more (2 a, 2 a', 2 c, & 2 c') were 

 then added, at the side of these, as shown 

 in the diagram (fig. 4, p. 61). 



In this manner successive fours followed 



1 ' The Primary Septal Plan of the Eugosa ' Ann. Mag. Nat. Hist. ser. 7, 

 toI. xviii (1906) pp. 356-03. 



