FISH-LIVERIES, AND WHY THEY ARE WORN. 77 



roundings, no indication has as yet been given 

 which will explain why the change takes place 

 so soon as a lack of harmony is established. 

 That is to say, how the various colour cells of 

 the fish, or other animals which change rapidly, 

 are affected by the colour of the world outside. 

 Much has yet to be done by experiment before a 

 thoroughly complete answer can be formulated ; 

 but practically we may say these colour changes 

 are due to stimulations through the eye. This 

 is shown by the fact that instances are on record 

 where fishes which did not correspond in colour 

 either with their fellows or their surroundings 

 were found to be blind. 



Some colours may be what we might call acci- 

 dental. They represent waste products thrown 

 off from the blood, and the fact that they lend 

 their aid to more or less beautiful colour schemes 

 is an accidental result. Protective coloration 

 has probably resulted from the advantageous 

 disposition of this waste colouring matter, a 

 distribution determined by the needs of the 

 individual. Thus, to take a simple case, such 

 as that of a normally-coloured fish, one that is 

 white below and dark above, the silvery white 

 is due, we have seen, to the presence of crystals 

 of guanin. The dark coloration due to dark pig- 

 ments of various kinds, is derived, as some believe, 

 by decomposition of blood corpuscles. JSTow, it 

 is possible that the distribution of these was 

 originally diffuse, that is to say, not definitely 

 confined to one region, as in the fishes of to-cJay. 

 If this were so, it is certain that there would 

 have been great variation amongst individuals, 



