On the Mechanical Conception of Nature. 66 I 



white during seven months of the year, the Nor- 

 wegian hare during nine months, and the Green- 

 land hare throughout the whole year. If our 

 climate became transformed into an arctic one, 

 after a given time there would arrive a period 

 when the older coloration no longer possessed 

 any advantage over the occasional and singly^ 

 appearing white variations ; the winter days during 

 which the ground was covered with snow would 

 have become so numerous, that the protection 

 afforded to the white animals would be equal to 

 the protection enjoyed by the brown individuals 

 on the equally numerous days free from snow. 

 From this time forth the hares that were white in 

 winter would not be subjected to a greater deci- 

 mation by foxes, &c., than the brown individuals. 

 This period must however be represented as con- 

 sisting of one or more centuries, and it would be 

 strange if from the individual white hares, which 

 now had an equal chance of existing, some white 

 families did not become established. But the 

 state of affairs would gradually become reversed 

 the brown hares would experience greater deci- 

 mation, and wherever there were white families 

 these would possess an advantage in the struggle 

 for existence. It does not follow that the dark 

 individuals would be forthwith extirpated ; on the 

 contrary, the advantage in favour of the white 

 would be but small throughout a long period of 

 time, and these individuals would only gradually 



