IV THE COLOURS AND PIGMENTS OF CCELENTERA 85 
base of the tentacles of the common Actinia , and so 
on. These beads are little clusters, batteries, of sting¬ 
ing-cells, and are sometimes called nematospheres. 
In some of the large tropical anemones the tentacles 
are greatly branched after the fashion called pinnate, 
and some of the pinnae are modified to form nemato¬ 
spheres, which are thus borne like little fruits on the 
surface of the tentacles. These are especially well 
developed in Heterodactyla , and there display the 
most wonderful beauty of colour. Often they are 
a brilliant translucent violet, with an apical spot of 
vivid emerald-green ; in another species they are a 
bright amethyst with a terminal spot of a darker 
tint. These nematospheres occur in clusters, and 
when viewed under the low power of the microscope, 
may, according to Mr. Saville Kent, “ be appropriately 
compared to currant-like fruit, carved out of amethyst, 
with a crystal of amethyst inserted, to represent the 
cicatrix of the antecedent flower.” The occurrence 
of such detailed beauties of form and colour in these 
simple organisms is of great theoretic interest. 
Among other interesting organisms included in the 
Ccelentera we must notice the blue coral ( Heliopora :). 
This obtains its name from the fact that its colour is 
more permanent than that of most corals, and the 
coloration is therefore quite marked in dried speci¬ 
mens. Curiously enough, the blue colour is more 
intense in the middle of the coral than on its outer 
surface, which is simply of a blue-gray colour. The 
polypes are small and pale-coloured. This form is 
of great interest because the special group to which 
it belongs, the Alcyonaria, do not now form as a rule 
continuous living skeletons, although many fossil 
