C. E. Beeches — Symmetrical Cell Development ui Favoaitidce. 217 



If these interstitial cells were to grow without the introduction of 

 others, until the original peripheral series was completely separated 

 from the parent or central cell, there would result a corallum con- 

 taining 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 it a twelve sided prism. 

 This stage is the third toward the formation of a series of mature 

 interstitial calices. 



During the third stage, the intermural buds increase in size until 

 they completely surround the parent cell. Then further growth 

 truncates their adjacent angles, thus adding two more sides to each 

 bud, making them pentagonal in section. This marks the fourth 

 stage of intermural growth. At the same time, the central corallite 

 loses six of its sides, and returns to its early hexagonal form. The 

 axes have revolved 30°, and the original sides have now become the 

 angles of the corallite, Plate XIY, figure 4. 



At this period of growth, it is necessary to consider a series of 

 buds on the periphery of the corallum, marked l", 2", etc., in Plate 

 XIV, figures 3 and 4, They are first triangular in form like the others, 

 and of two sizes, owing to their different ages. The growth of this 

 series continues until they touch and truncate the angles of the first 

 series (l', 2', etc.), producing the fifth condition or stage. The first 

 series of buds has now three hexagonal and three pentagonal coral- 

 lites, Plate XIV, figure 5. 



In the last or sixth stage, figure 6, the further growth of all the 

 intermural cells results in a corallum of nineteen nearly equal hexa- 

 gonal corallites. The original parent cell (1) is at the center, the 

 first six intermural cells (1', 2', etc.) completely surround it, and the 

 six new peripheral corallites (1", 2", etc.) are interposed between the 

 members of the original circlet (1, 2, etc.). The effect of this inter- 

 mural growth, then, is to dissociate all the first series of corallites 

 from the parent cell and from each other. 



The changes taking j^lace in the number and form of the cells 

 may be tabulated as follows : 



