HOW ANIMALS ADAPT THEMSELVES 25 



is spoken of as Variation. If among these in- 

 dividual peculiarities there is one which is in 

 any way disadvantageous, e.g. one which tends 

 to make the creature conspicuous in the sight of 

 its foes, the owner will be quickly eaten, and of 

 that peculiarity there will be an end. If, on the 

 contrary, the peculiarity gives the owner some 

 advantage over its fellows, that individual will 

 survive, and probably transmit its peculiarity to 

 some of its descendants. 



We have seen, for instance, that it is of ad- 

 vantage to our little periwinkle to be yellow, 

 when it lives in certain situations ; and that it 

 sometimes presents other colours, likely to be 

 favourable in other cases. If we gather together 

 a large number of specimens, we shall find a 

 surprising range of variation in colour. Some 

 present a tint of bright orange, nearly red ; some 

 are a dull brown ; the dark purple shade and the 

 drab have been already referred to. The very 

 young shell usually presents an unmistakable 

 shade of pink ; and we may find innumerable 

 half-grown specimens in which we may trace the 

 gradual establishment of the advantageous yellow 

 colour, from an original shade of unmistakable 

 pink, presented by the earlier whorls. Kindred 

 varieties of the shell, too, may be found with 

 stripes or speckles. Since this very common 

 shell may be found in abundance on any rocky 

 shore in the British Isles, the reader may easily 

 study its colour-variations, both in the dead and 

 the living shell. Study also the ground on which 

 the creature lives, with its sharp colour-contrasts 

 of rock and seaweed patches, and it will be easy 

 to understand why the colours are thus varied, 

 with a preponderance, on the whole, of the yellow 



