SYMMETRICAL CELL DEVELOPMENT IN FA VOSITID^ 433 



tively remote intervals, the corallum would have the form of 

 Rorrmigeria. In Michelinia convexa it is evident that, if the 

 divergence of the corallites was considerable and not wholly 

 filled by intermural growths, there would result a verticil of 

 corallites about the parent cell which would soon become 

 free. The peripheral corallites, also, would become separated. 

 Then after further growth the parent cell would give off 

 another verticil of buds, the other corallites, likewise, develop 

 similar verticils, and the whole form and mode of growth 

 would be like that of Romingeria. From this point of view, 

 Romingeria may represent an early form of symmetrical cell 

 development in the poriferous corals. The acceleration of 

 the periods of gemmation and consequent approximation of 

 the corallites carrying their verticils of buds would produce 

 all the conditions of cell growth and intermural gemmation 

 exhibited by Favosites or Michelinia. 



Nepionic. 

 First completed neanic 

 or first condition requi- 

 site to intermural gem- 

 mation. 



2d stage. 



3d stage. 



4th stage. 



5th stage. 

 6th stage. 



Form of primary cell. 



6-sided prism. 



9-sided prism. 

 12-sided prism. 



6-sided prism. 



6-sided prism. 

 6-sided prism. 



Number of 



sides of 



buds. 



Summary. 



The growth of intermural buds compensates for the natural 

 divergence of the corallites. New cells are introduced when- 

 ever the old corallites have reached their maximum size, and 

 when their divergence approaches a separation of the cell 

 tubes. 



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