SYMMETRICAL CELL DEVELOPMENT IN FA VOSITIDM 431 



necessary to illustrate the genei-al laws of iiiterraural growth. 

 The buds produced from any given cell cannot always agree 

 with the symmetrical method here described, on account of 

 the crowding of similar series from adjacent or neiglibor- 

 ing corallites. After eliminating these variations, it was 

 found that the process of intermural gemmation in general 

 is quite uniform, and closely conforms to that in Michelinia 

 convexa. 



Plate XXXII, figure 1, represents diagrammatically the 

 top of a corallum composed of a central parent cell and six 

 equal peripheral buds, making seven nearly equal calices in 

 the corallum. The upward growth of these corallites and the 

 divergence due to the direction of their axes tend to separate 

 them from the parent cell. In consequence of this separation 

 of the corallites, they would naturally assume a cylindrical 

 form, and there would thus appear triangular interspaces 

 between the tangent points of any three adjacent calices. 

 These angles, therefore, afford the only opportunities for the 

 introduction of a set of intermural buds, and their initial 

 triangular form is determined by the conditions of growth. 

 The smallest number of buds which can be symmetrically 

 placed, and compensate for the divergence of the corallites, is 

 three, one from each alternate angle of the hexagon (Plate 

 XXXII, figure 2). 



If these interstitial cells were to grow without the introduc- 

 tion of others, until the original peripheral series was com- 

 pletely separated from the parent or central cell, there would 

 result a corallum containing only triangular corallites. There 

 is, however, a manifest tendency of the organism to the 

 production and maintenance of a cylindrical form, or of a 

 prism with nearly equal radial axes, as in a hexagonal or 

 polygonal prism. To accomplish this, and further to take up 

 the divergence of the corallites, three new interstitial buds 

 are introduced at the remaining three unmodified angles, as 

 shown in figure 3. At this stage there are six symmetrically 

 disposed triangular buds, or intermural cells, about the 

 central corallite, truncating its original angles, and making 



