4 ANIMAL COLOEATIOX. 



Eclectm 'polychlorus this sexual dimorpliism is extremely 

 marked. It would be an exceedingly anomalous fact if the 

 same species of bird were to possess different pigments in tbe 

 two sexes ; and as a matter of fact it is not so in this parrot, 

 different in colour though the two sexes are. The same 

 pigments are present, but the structure of the feathers is 

 different, and thus the resulting colour as seen by the eye is 

 different. 



Different colours may be also produced by a variation in 

 the amount of the pigment present : the colours are darker 

 if a great deal of pigment is present ; and if there is but little, 

 the colour of the internal organs may show through the 

 comparatively transparent skin, and by their admixture with 

 the proper pigment of the skin produce a totally different 

 effect. The varying colours of many earthworms, leeches, and 

 other invertebrates, are instances of this. 



It is commonly said that there is no white pigment in 

 animals : this statement appears to be erroneous. Mr. Gaskell 

 finds that the pineal eye of the lamprey has white pigment. This 

 is also the case with the butterfly Arge galathea. The white 

 patches on the wings of this insect* turn yellow when ammonia 

 is applied to them ; as the ammonia evaporates the normal 

 white colour gradually returns. With fixed alkalies such as 

 sodium hydratte the primrose yellow colour was permanent, 

 but the white could be restored by means of acids. 



Pigment is present in other organs of the body besides the 

 skin: in the blood, for example, of red-(vertebrates, many worms) 

 and green- (certain worms — e.g. Sabella) blooded animals, and 

 in the liver. The colour of an animal is sometimes entirely due 

 to these internal pigments seen through the transparent and 

 colourless skin (e.g., pelagic ascidians, very small worms). 

 * Nature, 1884, vol. xxx., p. 571. 



