189 
Now, we have on record a case in which the sudden 
change took place in consequence of sudden exposure to 
extreme cold ; but the result was fatal, for the animal soon 
died. 
“A classical experiment made by Sir J. Ross, considerably over 
fifty years ago, seems decisive on the above-mentioned point, as far 
as the species experimented upon is concerned. A Hudson’s Bay 
lemming kept in the cabin, and thus shielded from the low tempera 
ture, retained its summer coat through the winter. It was accordingly 
placed on deck in a cage, on February ist, and next morning, after 
having been exposed to a temperature of 30° below zero, the fur on 
the cheeks and a patch on each shoulder had become perfectly white. 
On the following day the patches on each shoulder had extended 
considerably, and the posterior part of the body and flanks had 
turned to a dirty white ; during the next four days the change 
continued but slowly, and at the end of a week it was entirely white, 
with the exception of a dark band across the shoulders, prolonged 
posteriorly down the middle of the back. No further change took 
place, and the lemming died of cold on February 18th ; the ther 
mometer having been between 30° and 40° below zero every night.”— 
(Poulton. The Colours of Animals, p. 94.) 
This experiment shows how fatal it would be to a race 
to be subjected to changes of temperature sufficiently 
great to produce a transformation of colour in one week. 
And yet this is what is required if the race is preserved by 
the colour which conceals it. 
Another instance which is supposed to be peculiarly 
illustrative of the action of Natural Selection is to be 
found in the arctic white of animals inhabiting regions 
covered with perennial snow. “ The white appearance of 
arctic birds and mammals,” says Mr. Poulton, “must be 
advantageous for concealment in a region so largely 
covered with snow.”* Mr. Grant Allen says :— 
“Among the arctic snows a brown or black animal would imme 
diately be perceived, and, if defenceless, at once devoured ; while, 
if a carnivore, it would seldom or never approach unperceived near 
The Colours of Animals, f. 19.