outlining the size and shape of the ba?e of the soft parts of the 

 animal. At the same time the soft basal portion between the 

 mesenteries bends upward, permitting a greater deposit of Hme 



Fig. 47. — Vertical section through the edge of a very young stage of the coral, 

 Astroides calicularis, which has fixed itself to a piece of cork (r.). Very much en- 

 larged. The deposits of lime {b., ep.) are apparently thrown down outside the 

 ectoderm {ec.) but through the agency of these cells, b., basal plate ; ec, ectoderm ; 

 en., endoderm ; ep., epitheca ; mg., mesogloea ; m., mesentery ; s., septum, 

 developed by upward bending of wall of animal between the mesenteries (m.—m.) 

 upon the basal plate (b.). (Redrawn from Lankester's Zoology, after Von Koch.) 



here ; since the mesenteries radiate from the center to the edge 

 of the soft body portion so these ridges (septa) of calcium car- 

 bonate radiate likewise. These septal ridges grow higher and 

 higher, resulting finally in the thin septa, over each of which are 

 folded the three layers — ectoderm, mesogloea and endoderm. 

 The upper edges of the septa are conspicuously toothed, 

 giving them a saw-like appearance. The septa are seen to alter- 

 nate with the mesenteries but are external to the polyp, i.e. each 

 septum corresponds to a radial inpushing of the base and lower 

 sides of the polyp. The outer portion of the barrel-shaped 

 body of the animal early bends upw^ard faster than the inner 

 portion ; it thus results that the non-porous deposit of lime 

 thrown down by the ectoderm takes on a cup-like appearance, 

 called the calyx, with the septa extending from the edge of the 

 cup down to its center. Later the longest septa, expanding, 

 unite with one another to form a spongy, central mass, the 

 pseudo-columella . 

 As the animal grows in circumference and adds new mesen- 



