54 Colouration in Animals and Plants. 



colour that is still under personal control, as in the chameleon, &c., 

 is always hypodermal. 



The common crass (Bunodes crassicornis) is so extremely variable, 

 that all one can say of it is, that it is coloured red and green. But 

 this colour is distributed in accordance with structure. The base, 

 or crawling surface, not being exposed to the light, is uncoloured. 

 The column, or stem, is irregularly spotted, and striped in accord- 

 ance with the somewhat undifferentiated character of its tissue, but 

 the important organs, the tentacles, are most definitely ornamented, 

 the colour varying, but the pattern being constant. This pattern 

 is heart-shaped, with the apex towards the point of the tentacle ; 

 that is to say, the narrow part of the pattern points to the narrow 

 part of the tentacle. 



In the common Actinea mesembryanthemum, which is often blood red, 

 the marginal bodies, probably sense-organs, are of the most exquisite 

 turquoise blue colour, and the ruby disc thus beaded is as perfect an 

 example of simple structural decoration as could be desired. A zone 

 of similiar blue runs round the base of the body. 



Turning now to the corals, which are simply like colonies of 

 single anemonies with a stony skeleton, we have quite a different 

 arrangement of hues. No sight is more fascinating than that of a 

 living-coral reef, as seen through the clear waters of a lagoon. The 

 tropical gardens ashore cannot excel these sea-gardens in brilliancy 

 or variety of colour, Reds, yellows, purples, browns of every shade, 

 almost bewilder the eye with their profusion ; and here again we find 

 structural decoration carried out to perfection. The growing points 

 of white branching corals (Madrepores) are frequently tipped with 

 vivid purple, and the tiny polyps themselves are glowing gem-stars. 

 In the white brain-corals, the polyps are vivid red, green, yellow, 

 purple and so on ; but in almost every case vividly contrasting with 

 the surrounding parts, the colour changing as the function changes. 



The Alcyonarice, which include the sea-fans, sea-pens, and the red 

 coral of commerce, practically bring us to the end of the Coslenterata, 

 and afford us fresh proof of the dependence of colour upon structure 

 and function. The well-known organ-pipe coral (Ttibipora musica) 

 is of a deep crimson colour, and the polyps themselves are of the 

 most vivid emerald green, a contrast that cannot be excelled. 

 Almost equally beautiful is the commercial coral (Corallium rubrum) 

 whose vivid red has given a name to a certain tint. In this coral the 

 polyps are of a milk-white colour. 



