IV THE COLOURS AND PIGMENTS OF CCELENTERA 81 
accompanied by a process of contraction which not 
infrequently destroys all beauty of form as well as of 
colour. All these causes combine to render it practi¬ 
cally impossible, at least with present methods of 
technique, to adequately preserve the large majority 
of the Coelentera. Frequenters of museums will 
recall the glass models or crudely tinted chromo¬ 
lithographs which usually fill the cases devoted to 
the group. Although, therefore, the beauties of the 
coral-reefs must to most of us be merely a matter of 
hearsay, yet it should be emphasised that Coelentera 
are inhabitants of temperate as well as of tropical seas, 
and that many a pool on the British coast will dis¬ 
play organisms whose colouring differs in degree 
only, and not in kind, from that of the denizens of 
the most marvellous coral-reef. 
It is not necessary here to discuss the structure 
of the Coelentera ; we need only recall the fact that 
most of the organisms included in this class are either 
polypes of the nature of a sea-anemone, or jelly-fish 
of the familiar type, and that both these forms may 
occur in the course of a single life-history. For our 
purpose it is sufficient to think of a polype as con¬ 
sisting of a hollow column fixed at one end to some 
solid body, and bearing a mouth surrounded by 
waving contractile tentacles at the free end. Such 
polypes may grow singly as do the sea-anemones, or 
they may grow together in “ colonies.” The polypes 
in such colonies are connected together by a fleshy 
substance traversed by numerous tubes. If lime be 
laid down in considerable amount in this fleshy 
substance, the colony forms a “ coral.” This “ coral ” 
or limy skeleton is really outside the individual 
G 
