62 MOUNTAIN AND MOORLAND 



of being able to put on a white dress in the winter. 

 The Ermine, or Stoat (Mustela erminea), is an agile 

 carnivore, first cousin of the Weasel (Mustela vul- 

 garis), keen of sense, determined in the chase, cour- 

 ageous in attack. It feeds on Rats and Voles, young 

 Rabbits and Hares, and various birds, such as Grouse 

 and Ptarmigan. In the Highlands of Scotland the 

 reddish-brown Stoat always turns white in winter, be- 

 coming an Ermine ; and, as the change of colour does 

 not occur in Ireland and is rare in the South of Eng- 

 land, it seems safe to say that the cold is the external 

 cause that pulls the trigger. On the summit of Ben 

 Nevis white Stoats may be seen all the year round. 

 There is a twofold advantage in the blanching: it 

 gives the Ermine a garment of invisibility that 

 enables it to creep all unseen upon its victims, and it 

 supplies the Ermine with the kind of dress that loses 

 least heat in very cold surroundings. When the out- 

 side temperature is much lower than that of the body, 

 there is less animal heat lost from a white dress than 

 from a similar dress of any other colour, and the diffi- 

 culty that rises in the mind when we think of the 

 white dresses that we put on in the summer dis- 

 appears when we notice that white absorbs less of the 

 external heat than any other colour, and that it is not 

 white fur that summer dresses are made of. But how 

 is the change of colour brought about? The true 

 answer seems to be that given by Professor MacGil- 

 livray, that when the winter comes on the red hairs 

 of the summer dress are gradually replaced by new 

 white hairs. Specimens in process of change are 

 often seen, partly white and partly brownish-red, and 

 the new white hairs are seen to be short and young. 



