68 
GUIDE TO THE. CORAL GALLERY. 
The tissues seldom remain soft ; they become impregnated with 
horny matter or with carbonate of lime, or both. The horny skeleton 
is continuous ; the calcareous consists of separate spicules more or 
less closely packed. 
The differences at different ages in the amount of lime deposited 
are well shown by the fine series of specimens of Isis (Case 14). 
Colonies formed by budding and provided with a skeleton may 
become of great length, as Juncella , or of great intricacy of inter- 
lacement, as Gorgonella ; the fine Gorgonella verricidata from Zanzi- 
bar should be noticed ; often they are of exquisite beauty, as the 
Galligorgia from Mauritius (Fig. 5) or the Hooker ell a from South 
Japan suffice to show. Sometimes there is a continuous skeleton, as 
in the noble red coral of the Mediterranean, good specimens of 
which, showing the coral polyps expanded, and explanatory diagrams 
of which are exhibited in Case 13. 
A particularly dense skeleton is developed in Heliopora (Fig. 6), 
the only living member of a group (Coenothecalia) which formed a 
large part of the coral fauna of Palaeozoic times. Long considered 
to be a Zoantharian, the affinities of Heliopora to the Alcyonaria 
were demonstrated by the late H. N. Moseley during the voyage of 
H.M.S. Challenger. This skeleton is remarkable for being always of a 
blue colour when collected on a reef ; but, as Mr. Stanley Gardiner’s 
collections show, the blue colour gets progressively paler as specimens 
are obtained from deeper and deeper water. 
In other Alcyonaria a reduction of the skeleton seems to have 
occurred, so that the axis is friable and breaks up into scattered 
spicules ; this is the case with Paragorgia arborea , a fine example of 
which from the coast of Norway is shown with an illustrative 
drawing as it appears during life, and a well preserved piece with 
the polyps partly extended. 
In the Pennatulidae reduction goes still farther, and little is left 
in the way of a skeleton save a horny axis, which extends along 
the whole of the colony ; a striking example is to be seen in the 
specimen of Osteocella on the south wall of the Gallery. 
Fine examples of Pennatula , Funiculina , and others are shown, 
as well as two beautiful plates of Umbellula encrinus , taken from the 
Report of the Norwegian North Sea Expedition. The curiously 
modified and kidney-shaped Renilla should be noticed. 
The general plan of the structure of the Octocoralla is shown by 
Mr. Berjeau’s water-colour drawing in the Gallery, which is shown, 
reduced to a third, in the accompanying figure (Fig. 7), where we 
