98 
ME. H. N. MOSELEY ON THE 
section 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 result- 
ing from such an arrangement at the meeting-points of every three or four contiguous 
tubes filled in with calcareous matter, forming rods or beams of hard tissue, which are 
elevated above the margins of the tubes into papilliform prominences. Milne-Ed wards 
distinguishes between the tabulae of the ccenenchymal tubes and those of the calicles, 
calling the first “traverses,” the second “ planchers horizontaux;” but these 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 16 of these so-called septa are to be counted not uncommonly. In the enlarged 
figure of a calicle (fig. 17, Plate 9) Mr. Wilde 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. 
The fine structure of the hard tissue of Ileliopora is in many respects similar to 
that of the coralla of Hexactinian corals. It is composed of doubly refracting 
calcareous matter, which has half-crystalline, half-fibrous structure. On transverse 
section, fig. 4. Plate 8, it is seen to be made up of a series of systems of radiating 
fibres, i. e. areas of calcareous tissue showing a radiate fibrous structure. In each 
system the fibres radiate from a central axis and diverge to fuse at the margin of the 
system with the margins of the contiguous systems, a suture-like line being often 
observable where' two systems join. The fibres are dispersed more or less in laminae 
which overlap one another. The radial fibrous structure is to be seen only in thin 
.slices or fragments of the coral viewed by transmitted light. The fracture of the coral is 
irregular and crystalline. The central axes of the systems correspond to the centres 
of the vertical beams already described, which are prolonged above on the surface of 
the coral into papilliform projections. In a vertical section of the corallum (fig. 11, D, 
Plate 9) these axes are seen to take a vertical course within the beams and branch 
beneath the newly formed buds of the ccenenchym. The fibres are seen starting from 
the axes, spreading right and left from them throughout the tissue, with a uniform 
inclination upwards (i. e. towards the surface of the corallum). In the plates forming 
the sides of the tubes (B, fig. 11, Plate 9) the sutures between the fibres meeting one 
another at an angle from the two systems are well marked. The appearance of a portion 
of the hard tissue, as seen under a high power, is shown in fig. 12, Plate 9, where the 
appearance of the overlapping laminae is to be remarked. In the corallum of Pocillo- 
pora definite rod-like prisms with polygonal ends are to be seen to exist by viewing these 
structures end on ; in Helio'pora such a definite structure apparently does not occur *. 
* The radiating components of the hard tissue are here spoken of as fibres to distinguish them from these 
well-marked prisms of which the hard tissue of Pocillojjora is composed. The exact nature of the radial striae 
seen in the tissue of the Heliopora I do not understand ; they seem to represent spaces between variously 
shaped splinters, as it were, of hard matter arranged so as to form lamina. 
