UABIXS Oi' TJIE NOUWEGIAN LEMMING, 31 



It waa impossible not to feel pity for these self-haunted fugi- 

 tives. A mer6 cloud rapidly passing over the sun affrighted 

 them ; the approach of horse, cow, dog, or man alike roused their 

 impotent anger ; and their little bodies were convulsively pressed 

 against the never-failing stone of vantage whilst they uttered 

 cries of rage. I collected five hundred skins with the idea of making 

 a rug, but was surprised to find that a portion of the rump was 

 nearly always denuded of hair ; and it was long before I discovered 

 that this was caused by that habit of nervously backing up against 

 a stone, to which I have already alluded. As this action is excited 

 by so slight and constant a matter as the passage of the shadow of 

 a cloud, I confess I am surprised not to find a natural callosity 

 rather than so constant a lesion ; and this is a point which seems 

 of some little importance in connexion with the whole subject of 

 undoubtedly inherited tendencies, of which migration is an example. 



Mr. Wallace* suggests that "the survival of the fittest " has 

 ])layed an important jiart in causing migration by giving an ad- 

 vantage to those animals which enlarge their breeding-area by 

 travel. The lemming, it is true, always breeds during migration ; 

 but if none return or survive, it is difficult to say what becomes 

 of the fittest. However, I shall shortly have to mention a theory 

 wliich may tide over the difficulty. 



The lemmings certainly do not visit my part of Norway at any 

 recurring period of years ; but every third or fourth year they may 

 be expected with tolerable regularity, though in variable num- 

 bers. Thus it is quite probable that some migrations may have so 

 far escaped notice as to give rise to the old idea that they took 

 place every tenth year. 



They are, however, always directed westwards ; and thus the 

 theory that they are caused by deficiency of food fails so far, that 

 these migrations do not take place in a southerly direction, by whicli 

 a larger supply might be obtained. M. Guyon {I. c.) suggested 

 that the course followed was merely that of the watershed. 

 However, this runs east as well as west, and follows valleys which 

 often run north and south for hundreds of miles, whereas the 

 route pursued by the Lemming is due west. At all events this is the 

 case in Norway, where they traverse the broadest lakes filled wjth 

 water at an extremely low tempcratiire, and cross alike the most 

 rapid torrents and the deepest valleys. 



"With no guiding pillar of fire, they pass through a wilderness 

 by night ; they rear tlieir families on their journey ; and the three 

 * NatuiT, 1874, vul. X. p. 459. 



