300 
MR. H. N. MOSELEY ON THE 
and the plications in the wall of the fully formed calicle are to a great extent * the 
result of this peculiar mode of growth. This will be understood by reference to Plate 9. 
figs. 16 & 17, and also to Plate 9. fig. 15, where at B a section of a newly formed 
calicle is given. 
In a newly formed calicle, thus, the cavity is comparatively shallow in the centre, but 
prolonged at the bottom all round into a series of tubular offsets. Into these tubular 
offsets the mesenterial filaments hang down in the fresh condition of the animals. On 
further simple growth the tube of the calicle becomes elongated, and receives a new 
uniform bottom in the shape of a tabula. As the calicle approaches maturity, the 
cells immediately around it become nearly occluded at their mouths by increased 
development of calcareous matter at its margin. In older parts of the corallum the 
mouths of all the tubes are rendered very small by the excessive thickening of their 
walls and of the beams of hard tissue bearing the projecting points. On a quickly 
expanding frond of the coral the mouths of the series of coenenchymal tubes, which are 
rapidly increasing, are disposed in almost regular straight or curved lines radiating 
towards the points of extension. In this condition the lateral walls of each line of 
cells frequently fuse, becoming common to the line and more developed and prominent 
than the transverse ones, and thus come to form long, delicate ridges with projecting 
points on their edges, running almost parallel to one another, and with troughs between 
them. In these troughs calicles may arise, being most irregular in outline at first, but 
gradually becoming shapely by taking in surrounding cells. In some cases the point- 
like prominences at the margins of the walls of the cells included within a newly formed 
calicle may be seen at the bottom of the calicle, maintaining a disposition parallel to 
that of the trough in which the calicle is formed. 
These lines of calicles may be termed lines of growth. The calicles show a more or 
less marked disposition in transverse curves, cutting these lines at right angles. 
The development of the Heliopora colony probably takes place somewhat as repre 
sented in Plate 9. fig. 15. The original calicle (A) increases in length and forms suc- 
cessive chambers, A', A", A'", A"", by developing tabulae. It gives off a series of buds 
from its margin, which become elongate tubes divided into compartments in the same 
way, and in their turn give off buds. New calicles are formed as at B in the figure. 
Formation of the Hard Tissue. 
Everywhere in the living portions of the coral applied to the surface of the hard 
tissues is found a layer composed of elongate connective-tissue cells. The cells are 
nucleate and are finely granular in appearance, and are frequently drawn out into fine 
filaments at the ends. These cells occur only in connexion with the hard tissue, 
excepting in the superficial layer of the mesoderm beneath the epidermis, Plate 9. 
fig. 10. In the median plates of the mesenteries, for example, where no calcareous 
* Not entirely, sometimes two plications can be seen corresponding to one lateral tube only in a young 
calicle. 
