THE WONDER OF LIFE 551 



many cases, e.g. pheasants, in wtich the brilUant color- 

 ation, which is in most cases ' nuptial ', is a constant 

 mascuhne character. 



In Summary. — ^The point that we wish to emphasize 

 in this brief survey of animal coloration is, that the pigment 

 substances are primarily waste-products, reserve-products, 

 or by-products of the animal's metabohsm, and that in 

 many cases the colours have no more significance for their, 

 possessors than the gorgeous autumnal tints of withering 

 leaves have for the tree — ^that is to say, none ! Similarly, 

 the structural features that cause iridescence and the hke 

 are primarily the ripple-marks of growth. Likewise, in 

 many cases, it seems probable that the colouring of special 

 parts of the body is due to particulate conditions in different 

 parts. Just as green vivianite may be deposited in the 

 bones of a gar-pike, because of certain physiological cpn- 

 ditions, so an island on the skin, the tip of an ear, the end 

 of a tail may have a special colouring. In many cases, 

 all theory apart, it is certain that the pigments have come 

 to play an important r61e in the internal economy of the 

 body, as in the case of haemoglobin. From this basis, 

 however, we must go on to the further step, that in the 

 course of ages of variation and selection, certain arrange- 

 ments of pigmentation and markings have been caught up, 

 as it were, into the service of the animal's struggle for 

 existence, and utiUzed, often with extraordinary subtlety 

 and effectiveness, in concealment, in advertisement, as 

 aids in recognition, and as auxiharies in courtship. But 

 to look everywhere for secondary utihtarian justification 

 is quite gratuitous. 



An interesting case of coloration is found in a sea-urchin, 

 Echinus angulosus, common on South African coasts and 



