REPORT ON CORALS—HELIOPORID A. 107 
mesenterial filaments hang down in the fresh condition of the coral. 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 tubes 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 
which bear the projecting points. On a quickly expanding frond of the coral the mouths 
of the rows of coonenchymal tubes, which are rapidly increasing in length, are disposed 
in almost regular straight or curved lines directed towards the points of extension. In 
this condition the lateral walls of the tubes of each line frequently fuse, and become 
common to the line, and being more fully developed and prominent than the transverse 
walls, come thus 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 becom- 
ing 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 has been formed. 
These lines of tubes may be termed lines of growth. The calicles show a more or 
less marked disposition in transverse curves, cutting the lines of growth at right angles. 
The development of the Heliopora colony probably takes place somewhat as repre- 
sented in Plate IL. fig. 9. The original calicle (A) increases in length and forms succes- 
sive chambers, A’, A”, A’’”, A”, by developing tabulee in its interior. It gives off a 
series of buds from its margin, which become elongate tubes divided into compartments 
in the same manner, and which in their turn give off buds. New calicles are formed as 
at B in the figure. 
Mode of Deposition of the Hard Tissue in Heliopora caerulea. 
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 connection with the hard tissue, excepting in the super- 
ficial layer of the mesoderm beneath the epidermis, Plate IL. fig. 4. In the median plates 
of the mesenteries, for example, where no calcareous matter is formed, they are wanting, 
and homogeneous connective tissue alone present. It seems hence almost certain that 
they are the instruments of formation of the calcareous tissue. The newly-formed and 
growing points of the corallum yield much more organic remains after treatment with 
