STRUCTURE AND RELATIONS OF CERTAIN CORALS. 
123 
Description op the Plates. 
Illustrating the structure of Heliopora coerulea and Sarcophyton, sp. 
Al l the drawings, with the exception of figs. 16 & 17, Plate 9, are by the author of 
the paper. Figs. 16 & 17, Plate 9, are by Mr. J. J. Wilde. 
PLATE 8. 
Fig. 1. Schematic representation of a section vertical to the surface of Heliopora 
coerulea , showing the relations of the hard to the soft parts : the hard parts 
are coloured dark. In the centre is seen in section a fully developed 
sexually mature polyp in a retracted condition. The calcareous calicle in 
which it is contained is closed beneath by the tabula (CT), and the walls of 
the calicle are continued above into points (P) projecting above the general 
surface of the coral, the section being supposed to be so carried as to pass 
through two of the calcareous projections which surround the calicle. 
Closely applied to the surfaces of the calcareous tissue, and lining its 
cavities everywhere, is a layer of spindle-shaped connective-tissue cells, 
between which and the layer of entodermic cells is an interval occupied 
by transparent homogeneous connective-tissue. 
The layer of epithelium (E) covering the whole surface of the coral is 
seen to be continuous with that covering the exterior of the tentacles 
(here, from the introversion of those organs, appearing as their interior), 
whilst the entodermic layer (EN) covers their interior. The tentacle on 
the right side of the drawing has its tip passed behind the retractor muscle, 
Daxa states (U.S. Expl. Exped. vol. vii. Zoophytes, J. D. Dana, Philad. 1846, p. 539) that the blue colour 
of Heliopora is of animal origin and is lost on immersion of the coral in nitric acid. The colouring-matter was 
not analyzed by Air. Sillimax. 
In the Atlas of the ‘Voyage de l’Astrolabe,’ Zoophytes, pi. 29. figs. 12, 13, 14, the expanded polyps of 
Heliopora coerulea are figured by MM. Hombeox and Jacotinot. In fig. 14 sixteen very short, simp ly conical 
tentacles are shown, in fig. 13 only fifteen tentacles. The figures are evidently very erroneous. The corre- 
sponding description I have been unable to refer to, the volume containing it being wanting in the Hawaiian 
Government copy. 
In the Zoology of the ‘Voyage de l’Uranie,’ Qtjoy and Gaimaed, Paris, 1824, p. 656, is a description of the 
polyps of Heliopora ( Pocillopora ) coerulea. 
The expanded polyps have radiated tentacles, and are said to entirely hide the corallum when they are in an 
expanded condition. Experiments proved that the communication between the animals is somewhat imperfect, 
since a stimulus applied to any part of the colony caused only the polyps in that immediate neighbourhood to 
retract themselves. 
In the plates of the ‘Voyage de l’Uranie, ’ pi. 96. figs. 5, 6, 7, Heliopora is figured, showing in fig. 5 the 
appearance of the coral in the fresh state, but without any representation of the polyps. 
MDCCCLXXVI. S 
