218 C. E. Beecher — Symmetrical Cell Development in FavositidoB. 



stages. 



Nepionic. 

 First completed nea- 

 logic or first con- 

 dition requisite to 

 intermural gem- 

 mation. 



2d stage. 



3d stage. 



■Ith stage. 



5th stage. 

 6th stage. 



I I Number of Number of 



Form of primary cell. Whole No. intermural! sides of 

 of cells. buds. buds. 



cone. 



6 sided prism. 



9 sided prism. 



12 sided prism. 



6 sided prism. 



6 sided prism. 

 6 sided prism. 



7 



11 

 16 



19 



19 



19 



Buds are developed in Favosites and Michelinia whenever there 

 is a space or opporUinity for their growth, unless the corallum is 

 affected by some abnormal condition. If this tendency to form a 

 solid mass of corallites were not so strong, and if the process of 

 budding took place only at comparatively remote intervals, the 

 corallum would have the form of Romingeria. It is evident in 

 Michelinia convexa, 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 be- 

 come separated. Then after further growth, the parent cell Avould 

 give off another verticil of buds, the other corallites, likewise, 

 develop similar verticils, and the whole form and mode of growth 

 be like that of Momingeria. From this point of view, Bondngeria 

 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 ver- 

 ticils of buds, would produce all the conditions of cell growth and 

 intermural gemmation exhibited by Favosites or 3Iichelinia. 



Summary : — The growth of intermural buds compensates for the 

 natural divergence of the corallites. New cells are introduced 

 whenever the old corallites have reached their maximum size, and 

 when their divergence approaches a separation of the cell tubes. 



The form of the buds is first that of a triangular pyramid or prism, 

 and is due to the mechanical conditions of growth. During subse- 



