344 THE EVOLUTION THEORY 



Early in these lectures we discussed the twofold protective value 

 of the coloration of the 'variable hare' {Lepv^s variabilis), which 

 is distributed over the Arctic zone of the Old and New World, and 

 also occurs in the higher regions of the Alps. Wherever there is 

 a sharp contrast between winter and summer the variable hare 

 exhibits the same specific type, being brown in summer and white in 

 winter, but in regard to this very character of colour-change it forms 

 races to some extent, for it is white for a longer or shorter time accord- 

 ing to the length of the winter — in Greenland for the whole twelve 

 months of the j^ear, in Northern Norway only for eight or nine 

 months, in the Alps for six or seven months, but in the south of 

 Sweden and in Ireland not at all. There it remains brown in winter 

 like our common hare (Lepus timidus). This is not a question of the 

 direct effect of cold ; if it were the species would become white in 

 Southern Sweden also, for there is no lack of severe cold there, but 

 the ground is not so uninterruptedly covered with snow, and so the 

 white colour of the hare would be as often, probably oftener, a danger 

 than a safeguard, and the more primitive double coloration has 

 therefore been done away with by natural selection. The change 

 of colour is thus hereditarily fixed, as is proved by the fact that 

 the Alpine hare, if caught and kept in the valleys below, puts on 

 a white dress at the usual time, which the common hare never does. 



As in Southern Sweden the winter coloration has been wholly 

 eliminated, so, conversely, from there to the Arctic zone the summer 

 colouring has been more and more crowded out, and in the Farthest 

 North it has totally disappeared from the characters of the species. 

 We thus see that wherever the species lives the double colouring is regu- 

 lated, as regards the duration of the winter coat, in exact harmony with 

 the external conditions. There is a pure white, a pure brown, and 

 a colour-changing race, and the latter is subdivided into two — one 

 wearing the winter dress for six, the other for eight months. 

 Probably these could be still further subdivided, if the different 

 regions of the Scandinavian Peninsula were investigated individually 

 from south to north. That the duration of the winter dress has its 

 roots in the germ-plasm, and does not depend solely on the earlier or 

 later period at which the cold sets in, is made clear by the two 

 extreme forms, the white and the brown Lepus variabilis, as well as 

 by the behaviour of captive animals. The familiar case of Ross's 

 lemming, which remained brown in the warm cabin, and then 

 suddenly became white when it was exposed to the cold of winter, 

 only shows that the cold acts as a liberating stimulus. The pre- 

 paratory changes in the pellage are already present, and the stimulus 



