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STEUCTUEE AND EELATIONS OF CEETAIN COEALS. 
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B. Portion of wall of tube cut parallel to its surface, showing a line of 
suture between the fibres of opposite systems composing it. 
D. Vertical canal. 
P. Point of growing coral, showing lines of successive growth. 
The numbers indicate the order in which the successive chambers 
were formed. 
Fig. 12. Portion of the hard tissue forming the wall of a tube-cavity of Heliopora 
ccerulea , from the same preparation as fig. 11, more highly magnified. 
C. Axis. 
B, and similar shaded bands on the other side of the axis. Part of the 
tissue stained of a more intense blue than the remainder. 
Fig. 13. 
Fig. 16. 
Fig.JIT. 
a, a. Two of the cells of the entoderm of Heliopora ccerulea ; one of these 
with the contents undergoing fission. 
V . Nematocysts of the same. 
b. A form in which they are commonly to be observed, with the thread 
partly protruded and curved in a loop, and with one side of the cell 
bulged in. 
Ovum of Heliopora ccerulea as attached to the mesentery. 
Diagram to show the growth of Heliopora by successive budding and develop- 
ment of tabulse. 
A. The original calicle of the stock: A', A" &c., successively formed 
chambers in continuation of this calicle ; 1, 2, 3, successive 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 calicular cavity 
is formed with the original short tube at its bottom. 
Drawing by Mr. J. J. Wilde, Artist to the ‘ Challenger’ Expedition, of a rapidly 
growing tip of a frond of Heliopora ccerulea. 
The young growing tubes of the ccenenchym are polygonal in area. 
A A. Calicles in various stages of formation. 
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. 
