Piiiimrij S('j>f<(/ /'/(tu ('/the fiuijusa. 



:iy.) 



SlacjcW. — Two new septa arc next .seen to arise, one on 

 eacli side of the " main " end of tlie axial scptutn. Thou^^li 

 remaining- attached to tlie wall of the caliclc and to the axial 

 se|)tiim, they o-i-uhially spread outwards, and eventually 

 form the *' alar'' primary septa oi Kunth (diag. A. 2). 



Diiigrniu A. — rorinalioii of Si'pta in a .Simple Rugose Coral. 



I 2 "^2 2^„-T~N.2 



3 3 ' 3 



1-4. Development of the Piimaiy or Protosepta. 



• 3^-f — H 



5 6 7 



5-7. Development of the Secondary or Metasepta. 



Stage III. — Shortly after the alar primaries have deveh^ped 

 another pair appears, in the same manner as before, but at 

 the opposite or " counter " end of the axial septum 

 (diag. A. 3). These also spread outwards, though very 

 rarely to the same extent as the alar septa. There is now a 

 distinct pause in the formation of new septa, and no more 

 appear for some time. Any irregularity that there may have 

 been previously in the growth of the septa is corrected at this 

 stage, and the two hiteral pairs dispose themselves symme- 

 trically on each side of the axial line* (diag. A. 4). Later 

 septa are added on a slightl}' different plan. As before, they 

 appear at the junction of the last-formed septum Avith the 

 wall and in pairs, but in.stead of moving towards each other 

 as the two lateral primary pairs did, they all eventually move 

 towards the counter septum, and all arise on the fossular 

 faces of the last-formed septa (diag. A. 5, 6, & 7). No 

 further description of the development of these later septa 

 need be given here, as this part of the subject has been fully 



* The six protosepta are rapidly developed. An opaque microscopic 

 section (U. 5-5) shows very clearly the beginning of Stage II. on one side 

 and the close of Stage III. ou the other, although the section is less than 

 •o mm. thick. 



