390 Dr. .1. E. Duel (Ion on the Iielationshii>s 



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Fio. 7. 



Transverse section towards the upper region of a fourth individual coral 

 before the projecting columella becomes free from the septa. The 

 middle of the section is occupied by the large columella with which 

 the septa are fused ; the different centres of calciticalion show that 

 the columella at this region is formed of the fused enlarged middle 

 extremities of the chief septum and the lateral septa. The section is 

 of particular interest as showing the late ajipearance of the email 

 alternating septa. In all the previous sections no trace of these was 

 present, but they aie here represented by dark centres of calcification 

 within the thickened thecal v\all. A septum occurs between every 

 two adjacent larger septa, so that the totnl number of septa now 

 corresponds with the number of superficial grooves ; in higher sections 

 and in mature corallites the small septa are .seen as distinct projec- 

 tions from the inner surface of the wall. The additional smaller 

 eepta therefore appear practically simultaneously, and only when 

 prowth is nearly completed ; they have thus no sequence value what- 

 ever ; only the larger sejita are of importance in this direction. The 

 section alieady shows the formation of the septal fo.«8ula by the 

 coalescence of the two interseptal chambers, one on each side of the 

 counter septum. 



interspaces, and in the adult never assume a cyclical ar- 

 rangement, but remain bilateral. It is the first cliaracteristic 

 which fundamentally distinguishes the form from any known 



