2S2 COLOUR IN NATURE chap. 



describes a considerable number, differing from one 

 another by their spectra, their solubilities, or their 

 reaction to light. It does not appear that any good 

 purpose would be served by giving a list of these 

 pigments, at least in our present state of ignorance 

 as to the relations of the lipochromes. It is sufficient 

 to note that yellow lipochromes occur very frequently 

 in the skin, the fat, the yolks of the eggs, and the 

 feathers of birds ; that these yellow lipochromes 

 not infrequently occur mingled with zoonerythrin, 

 that yellow feathers may contain two different 

 yellow pigments, and that these yellow pigments 

 may also be present in feathers which contain too 

 much dark pigment for the yellow colour to be 

 visible. The appearance of the feather is thus no 

 certain criterion of the presence or absence of lipo- 

 chrome pigment. 



An exceedingly curious instance of this is afforded 

 by Krukenberg's researches on the colouring-matters 

 of Eclectus polychlorus. In this interesting parrot the 

 male is chiefly green, with patches of red and blue ; 

 the female is chiefly red, with patches of yellow and 

 blue ; while, according to Meyer, the young of both 

 sexes are red. The blue and green feathers are 

 grayish-black on their lower surfaces and appear 

 dull-coloured by transmitted light ; the yellow and 

 red do not change colour by transmitted light. The 

 pigments present are one or more dark-coloured 

 melanins, a yellow lipochrome, zoofulvin, and red 

 " araroth " ; the colour differences are in part due to 

 structure, in part to the varying amounts of the pig- 

 ments in the two sexes. This is shown in the 

 following table : — 



