The Making of Species 



To sum up, the observed facts of animal 

 colouration seem to indicate that there are in 

 each organism some twelve or thirteen centres of 

 colouring, which we suggest may correspond with 

 portions of the fertilised egg. From each of 

 these centres the colour develops and spreads, 

 so that every part of the organism is eventually 

 coloured. These centres of colouring are not 

 altogether independent of one another. Some- 

 times they all give rise to the same hue, in which 

 case we have a uniformly-coloured organism, such 

 as the raven. More often from some one colour 

 develops, and from others another colour ; if 

 these two colours happen to be black and white, 

 the result is a pied organism, which displays a 

 definite pattern due to the correlation of the 

 various colour-producing biological molecules. 



Thus it occasionally happens that two widely 

 different organisms exhibit very similar mark- 

 ings, and therefore resemble one another. When 

 this resemblance is believed to be of advan- 

 tage to one or other of the similarly-coloured 

 species, naturalists call it mimicry, and assert that 

 the likeness is due to the action of natural selec- 

 tion ; but where neither organism can profit by 

 the resemblance, zoologists make no attempt to 

 explain it What we suggest is that the coloura- 

 tion of an animal depends upon the structure, or, 

 at any rate, the nature, of the parts of the egg 

 which produce these centres of colour. But this 



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