X THE COLOURS OF FISHES 209 



and colouring there is a remarkable uniformity of 

 pigments. With a few exceptions, turacin being per- 

 haps the most important, the pigments seem to be all 

 either lipochromes or melanins, the lipochromes pre- 

 dominating in fishes, amphibians, lizards, and birds, 

 the melanins in snakes and mammals (Krukenberg). 

 As the melanins are often regarded . as derivatives 

 of haemoglobin, and the lipochromes of fats, some 

 would say that there are two kinds of pigments in 

 Vertebrates- — effete blood pigments and modified fats 

 (see Kiikenthal). Secondly, in many cases the 

 general coloration is due either to structural effects 

 or to the patterns and markings rather than simply 

 to the pigments themselves. The development of 

 structural colours is associated with the degree of 

 development of the cuticular outgrowths, and reaches 

 perhaps its greatest height in birds. In mammals 

 bright structural colours are rare, and the frequent 

 beauty of colour is due solely to the unequal 

 distribution of the melanin pigments which gives 

 rise to bands or spots. Eimer has endeavoured to 

 prove that in all Vertebrates longitudinal markings 

 are the most primitive form of coloration, and that 

 spots, transverse stripes, or uniform coloration are 

 secondary derivatives. His work on the Markings 

 of Animals shows, at least, that there is an 

 extraordinary constancy in the markings which run 

 through orders, as is, for example, well seen in the 

 Carnivora among mammals. 



Sexual dimorphism of colour is another char- 

 acter which is exceedingly common among Verte- 

 brates. This may manifest itself simply in the 

 greater brightness or purity of tint in the male as 



p 



