The Making of Species 



up elaborate theories on very slender foundations 

 is a too frequent failing of zoologists. We desire 

 merely to emphasise the fact that the phenomena 

 of animal colouration almost force us to the con- 

 clusion that the colouring of each organism is the 

 result of the development of a number of units. 



It may be objected that, if this be the case, the 

 number of the units which contribute to the colour 

 of any organism must be exceedingly large, since 

 we see in nature an almost limitless number of 

 different schemes of colouring. If the colour of 

 each animal be the result of the development of 

 a few units, it might be thought, firstly, that the 

 diversity of schemes of colouration which we 

 observe in nature could not possibly occur ; 

 and secondly, that, under such circumstances, 

 the colour pattern of a bird or beast should 

 be of the nature of a mosaic, each colour being 

 sharply defined and separated from every other 

 colour, instead of the colours shading one into 

 the other, as is so frequently the case. 



Such objections would be based on a miscon- 

 ception as to the nature of the units which com- 

 bine to produce the colouration of an organism. 

 These units show themselves as centres of develop- 

 ment of colour, as points from which the colour 

 or colouring they represent spreads, until it 

 meets and mingles with other patches of colour 

 which are being developed from other centres. 

 The colour produced at one centre may spread 



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