104 THE VOYAGE OF H.M.S. CHALLENGER. 



lobulate, anil rising in a tuft. Ccenenchym very abundant, and presenting at its surface 

 a great number of rounded pores disposed with regularity and separated by projecting 

 papilliform grains. These grains are formed by the upper extremities of an equal number 

 of cylindrical and vertical beams, which shut in tubuliform spaces, open above, and 

 divided from space to space by cross partitions. Calicles circular. Septa very little 

 developed, but distinct, and twelve in number. Horizontal floors present and well 

 developed. The genus is remarkable for its alveolar appearance and the tubular 

 structure of the parenchym." 



The coral is figured by Milne-Edwards, I.e. (pi. i. fig. 3, a-c). A drawing of the 

 growing tip of a frond, much enlarged, will be found on Plate II. figs. 10 and 11 of this 

 paper. The following points require to be remarked concerning the structure of the 

 corallum. The papilliform eminences described by Milne-Edwards as covering the sur- 

 face of the corallum spring from the points of apposition of the walls of several of the 

 ccenenchymal tubes, very usually from the point of meeting of the mouths of four tubes 

 (PL II. fig. 11). At these points the hard tissue consists of thickened vertical beams of 

 calcareous matter, from which thin lamellar-like processes are given off. These processes 

 form the walls between two contiguous tubes by crossing to join similar processes from 

 adjacent beams. Each beam thus gives off four lamellar processes, which are disposed 

 roughly at right angles to one another. The narrow summits of the thin laminae forming 

 the sides of the tubes fall short in their centres, by a considerable distance, of the level 

 of the thickened masses from which they spring, and are excavated or hollowed out at 

 these spots. It is across these excavations in the laminae that the canals of the deep 

 system pass in the fresh condition of the coral, by means of which the cavities of the 

 tubes and polyps communicate freely with one another. The structure of the ccenen- 

 chym of the coral might perhaps be better described by saying that it consists of a series 

 of tubes of cirevdar section, and of nearly uniform diameter, closely packed side by side 

 more or less in regular rows, with their walls where touching fused together, and the 

 spaces necessarily resulting from such an arrangement at the meeting-points of every 

 three or four contiguous tubes filled in with calcareous matter, so as to form rods or beams 

 of hard tissue, which are elevated above the margins of the tubes into papilliform promi- 

 nences. Milne-Edwards distinguishes between the tabulae of the ccenenchymal tubes and 

 those of the calicles, calling the first " traverses," and the second " planchers horizontaux," 

 but they are essentially similar structures. Though twelve is a common number for the 

 projecting plications of the margin of the mouth of the calicle, the number is very 

 variable — 11, 13, 14, even 15 or 1G of these so-called septa are to be countod not 

 uncommonly. In the enlarged figure of a calicle (PI. II. fig. 11) Dr Wild has drawn 

 fifteen. The plications become less numerous at a slight depth in the calicle, and 

 often here are only eight in number, with a mesentery of the polyp passing to each 

 internal projection. 



