IV THE COLOURS AND PIGMENTS OF CCELENTERA 85 



base of the tentacles of the common Actinia, and so 

 on. These beads are httle 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 ilower." 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 

 Coelentera we must notice the blue coral {Heliopord). 

 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 



