44 CORALS AND CORAL L8LAND8. 



from specimens collected by him at a depth of 100 to 200 

 fathoms off the Florida reef. The actual size was one-third 

 that of the figure. The second figure represents a living 

 species. 



The bottom of the calicle, or polyp-cell, in the corallum is 

 sometimes made simply by the meeting of the radiating sep- 

 ta; occasionally by the same, with the addition of a point 

 or columella at the centre ; often by a twisting together of 

 this part of the radiated septa. Very often, also, it is a mere 

 porous mass. Sometimes there is a circle of prominent points 

 about the centre, as seen in the figure of a Caryophyllia on 

 page 42, which are the extremities of narrow vertical strips 

 (called pali) lying in the planes of the septa. Similar points 

 exist in the Thecocyathus on the preceding page, though not 

 in sight in the figure. 



In many cases the bottom is quite solid ; and this may be 

 so either (1), because the coral secretions fill up all the pores 

 as the polyp increases in age, and thus make the inte- 

 rior of the corallum solid or nearly so ; or (2), because there are 

 formed periodically, as the polyp grows upward, solid horizon- 

 tal plates across the bottom, so that beneath, in the interior of 

 the corallum, there is a series of plates or tables with spaces 

 between. The Pocilloporse, among recent corals (p. 70), and the 

 Favosites among ancient, are examples. Increasing solidity 

 with the increasing age of the polyps is also produced at 

 times by additions to the exterior of a corallum. In many 

 species, the skin, over part or all of the exterior, gradually 

 disappears or dies away and leaves the corallum bare, while 

 all is living within ; and, in such cases, the skin, before disap- 

 pearing, often adds a layer of stony material to the exterior, 

 giving greater firmness to the whole. An example is shown 

 in the figure on p. 41. In such a case, there is no skin or 



