REPORT ON CORALS — EXPLANATION OF PLATES. 237 



A. Former ; A', recent calicular cavity. 



C, C. Tabula. 



B. Portion of wall of tube cut parallel to its surface, in which a line of 



suture between the fibres of opposite systems composing it is to be 

 observed. 



D. Vertical canal. 



P. Point of growing coral showing lines of successive growth. 



The numbers 1, 1'; 2, 2", &c., indicate the order in which the succes- 

 sive chambers were formed. 

 Fig. 6. Portion of the hard tissue forming the wall of a tube cavity of Heliopora cceridea, 

 from the same preparation as fig. 5, more highly magnified. 



C. Axis. 



B. Shaded band caused by the fact that part of the calcareous tissue is 

 stained of a more intense blue than the remainder. A similar band is seen 

 on the opposite side of the axis. 

 Fig. 7. a, a Two of the cells of the endoderm of Heliopora cceridea; one of these with 

 the contents undergoing fission. 



V Nematocyst of the same, b A form of nematocyst commonly to be 

 observed in which the thread is partly protruded and curved in a 

 loop, whilst one side of the cell is bulged in. 

 Fig. 8. Ovum of Heliopora ccerulea as attached to the mesentery. 



Fig. 9. Diagram to show the growth of Heliopora by a process of successive buddings 

 and developments of tabulae. 



A. The original calicle of the stock: A', A", &c, successively formed 



chambers in continuation of this calicle; 1, 2, 3, successive lateral 

 buds. 



B. Formation of a new calicle. A short tube buds out, but the tubes on 



either side of it grow more quickly. Only the outer part of their 

 walls continues to be developed ; hence a wide circular cavity 

 is formed with the original short tube at its bottom. 

 Fig. 10. Drawing by Dr J. J. Wild, Artist to the Challenger Expedition, of the rapidly 

 growing tip of a frond of Heliopora car idea. 



The young growing tubes of the ccenenchym are polygonal in area. 

 A A. Calicles in various stages of formation. 

 Fig. 11. By the same. A calicle nearly fully developed, as seen when looked directly 

 into. The calicle is surrounded by irregular dentations, of which there are 

 more than twelve. A circlet of ccenenchymal tubes is seen to join the cavity 

 of the calicle below. 



