REPORT ON CORALS—HELIOPORID. 109 
In no part of the growing points of the corallum of Heliopora is there any trace of 
the calcareous tissue being built up of the fusion together of a network of spicules, as 
occurs in the case of the corallum of Corallium rubrum and also in that of Tubipora, as 
was shown to be the case by Perceval Wright,’ and as may be seen at once by examining 
the growing end of the tube of a spirit specimen of Zubipora. In this respect 
Heliopora differs most markedly from both Corallium and Tubipora. The structure of 
the hard tissue of Heliopora is, however, in many respects very like that of the sclerites 
of Primnoa. 
Blue Coloration of the Corallum of Heliopora cerulea. 
The corallum of Heliopora is coloured of a deep blue, and has always been 
regarded as remarkable amongst corals for this fact. Now that it is known to be an 
Aleyonarian structure the fact is less exceptional, since both Corallium and Tubipora 
have a deeply coloured corallum, and many other Aleyonarians have coloured 
spicules. Amongst Madreporaria such a condition is exceptional, but the coralla 
of some Fungias and Desmophyllums is coloured madder red by a peculiar colouring 
matter which I have termed “ polyperythrin,”’ 
and which occurs also abundantly in 
many Medusze and other Coelenterata. In the case of certain Eupsammidee also the 
corallum is red. 
The blue tint is seen in sections of the corallum of Heliopora cerulea to be diffused 
within the hard tissue. The colour is faint or almost absent in the freshly-growing tips 
of the corallum, and pale in the most recently-formed superficial structures generally ; it 
is darkest in the layer lying immediately beneath these, that is to say, in the most 
recently matured tissue. In transverse sections it is seen to be darkest at the surfaces of 
the walls of the tubes and calicles. In vertical sections of the corallum the continuation 
of the dark blue line marking the margin of the wall of each tube enables the line of the 
tube to be traced past the superadded tabula, and marks the boundary between the two 
structures. Very exceptionally, intensely blue streaks are developed more internally on 
either side of the central canal, as in Plate II. fig. 6, where B marks such a blue band. 
The usual distribution of the colouring is that shown in Plate I. fig. 4, where the dark 
zone at the margin of each tube seen in section represents intense colouring. The tabule 
are almost colourless. 
When the corallum is boiled for a long period in caustic potash the blue colour 
remains unaltered. When the calcareous matter is removed from the corallum by means 
' J, Perceval Wright, On the Animal of the Organ-pipe Coral, Ann. and Mag. Nat. Hist., vol. iii. p. 377, 4 ser., 
1869. 
2 H. N. Moseley, On the Colouring Matters of various Animals, and especially of Deep-Sea Forms dredged by 
H.M.S. Challenger (Quart. Journ. of Micro. Sci., new ser., Jan. 1877, vol. xvii. p. 2). 
