THE WONDER OF LIFE 551 



many cases, e.g. pheasants, in which the brilliant color- 

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

 masculine 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 metabolism, 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 like 

 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 con- 

 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 1 

 to play an important role 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 utilized, often with extraordinary subtlety/ 

 and effectiveness, in concealment, in advertisement, as; 

 aids in recognition, and as auxiliaries in courtship. But * 

 to look everywhere for secondary utilitarian justification 

 is quite gratuitous. 



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

 Echinus angulosus, common on South African coasts and 



