INTRODUCTORY. 3 



birds is chiefly due not to one pigment, but to two apparently 

 distinct pigments, which give different chemical reactions; to 

 these two pigments their discoverer, Kriikenberg, has given 

 the name of Zoorubiu and Pseudozoorubin respectively. An 

 inspection of the feathers would not enable one to tell with 

 certainty which of the two substances was the cause of the 

 colour ; but an extract of zoorubin can always be detected by its 

 change to a beautiful cherry red on the addition of the minutest 

 trace of blue sulphate of copper. The green colour of the 

 feathers of the turacou is due to a pigment, turacoverdin, 

 which is quite different from that which causes the green colour 

 of the parrot.* Again, the crimson colour of the same bird is 

 produced by a very different pigment from those which cause 

 the crimson colour of any other birds the colouring-matter of 

 whose feathers has been studied. 



This being the case, it is not surprising to find that animals 

 only remotely allied are often coloured by quite different pig- 

 ments, which yet produce the same effect. 



But on the other hand there are some pigments which have 

 a very wide distribution among animals. Zoonerythrin, or 

 tetronerythrin, as it has been also called, is found in both 

 vertebrates and invertebrates. The blood of the common 

 earthworm owes its red colour to haemoglobin, as does also the 

 blood of all vertebrate animals, including man. 



Pigments may be even common to plants and animals : apart 

 from chlorophyll (see p. G), it has been stated that carotin (a 

 vegetable pigment) is found in certain Crustacea. 



Sometimes differently coloured animals have in reality the 



same skin pigments. The attention of the reader will be 



directed in a later chapter to the remarkable difference in 



colour between the males and females of certain parrots. In 



" The actual pigment here is yellow. 



