102 
ME. H. N. MOSELEY ON THE 
is the case in the corallum of Corallium rubrum and also in Tubipora, as may be seen 
at once by examining the growing end of the tube of a spirit specimen of Tubipora 
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. 
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 Alcyonarian 
structure the fact is less exceptional, since both Corallium and Tubipora have a deeply 
coloured corallum, and many other Alcyonarians have coloured spicules. Amongst Hexac- 
tinians Stylasterf rosaceus is of an intense red, and the corallum of some Fungias is also 
red ; also that of certain Eupsammidae, but amongst these the condition is exceptional. 
The blue tint is seen in sections of the corallum 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 be- 
neath these in the recently matured tissue. In transverse sections it is seen to be darkest at 
the surfaces of the wnlls 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 9. fig. 12, 
where B marks such a blue band. The usual distribution of the colouring is that 
shown in Plate 8. fig. 4, where the dark zone at the margin of each tube seen in 
section represents intense colouring. The tabulae 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 of hydrochloric acid, the colouring-matter is set free, and remaining suspended 
in the fluid gives it a blue tint. It is, however, not in solution, but can be observed 
under the microscope to exist in the fluid in the form of small, amorphous, intensely 
blue masses adhering to small shreds of tissue, &c., and in this condition may be proved 
to be insoluble in strong hydrochloric acid. If the coloured solution formed by hydro- 
chloric acid be filtered, the blue colouring-matter remains on the filter, and the filtrate 
has only a very slight greenish tint. 
* This fact concerning Tubipora seems not to be well known. Claus, l. c. p. 204, says : “ Unter Ausschluss 
von Kalkkorpern entstehen endlich die festen Kalkskelete der Tubiporen nnd sammtlicher Madreporarien.” The 
fact was well known, however, to Professor Wyville Thomson, who directed my attention to it. Prof. Thomson 
does not know, however, where the fact is published (he thinks possibly by Prof. Peeceval Weight in the 
‘ Ann. and Mag. of Nat. Hist.’). Disks of soft tissue spread from the mouths of the tubes of growing parts of the 
coral. The disks contain an open network of calcareous matter, evidently composed of fused spicules. The 
disks fuse with neighbouring ones and form the horizontal laminae. 
t Since the above was written I have proved the Stylasteridae to be Hydroids . — July 8, 1876. 
