EEPORT ON CORALS — HELIOPORID^. 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 ccenenchymal 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 II. fig. 9. The original calicle (A) increases in length and forms succes- 

 sive chambers, A', A", A'", A"", by developing tabulae 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 ccerulea. 



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 II. 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-fanned and 

 growing points of the corallum yield much more organic remains after treatment with 



