Jl-N-E -21, 1895.] 



SCIENCE. 



091 



on, i)rocecdin<;- liopelessly to certain death. 

 Tho direction of the march is dependent 

 on the valleys, and the exodus may '• radiate 

 in quite opposite directions from one and 

 the same mountain plateau. * * * * Thus 

 during migratory years the southern rami- 

 ficaticms of the Lang Fjeld will emit 

 swarms which may advance eastward as 

 far as the Christiauia Fjord ; southward, 

 down to the coastal regions of Christiauia 

 Stift; and westward, to the fjords in the 

 counties of Stavangcr and SiJndre Bergen- 

 luis. -■- -^ ■^- During the entire course of the 

 summer and autumn, they continue to pour 

 forth from the mountains. * =i= * * In the 

 valleys they invariably meet with lakes or 

 rivere, and large numbers constantly en- 

 deavor to cross them. If the mountains 

 are high on both sides, the valley will, as a 

 ride, receive contributions from each slope, 

 and individuals may be observed crossing 

 the river in both directions." 



" During the migrations they do not allow 

 themselves to be stopped by rivers, or even 

 by the arms of a fjord, but trust themselves, 

 without hesitation, to the mercy of the 

 waves, in order to reach the opposite shore. 

 It would almost seem as if uo stretch of 

 water were too wide for them to cross if 

 they but see land on the other side. During 

 the great migration in the district of 

 Trondhjem iu 1808, which has previously 

 been mentioned, a steamer on the Trondhjcni 

 Fjord steamed into a crowd of swimming 

 Lemmings of such vast extent that she took 

 over a quarter of an hour to pass through 

 it, and as far as one could see fi-om the 

 vessel down the fjord its waters were covered 

 everywherewith these animals. During the 

 great migratory years similar accounts are 

 received from all the great lakes (Mjosen, 

 Kandsrjord, Kroderen, etc., etc.)." 



Great havoc is wrought in meadows and 

 gi-ain fields by the hungry hordes, particu- 

 larlj- iu mountain pastures and farms situ- 

 ated on the higher slopes. 



It is stated tliat uo rule can be laid down 

 concerning the fre<iuency of the migratory 

 years. The greatest migrations, which ex- 

 tend down to the most distant lowlands, 

 take place but seldom and rarely occur in 

 the southern districts oftener than once in 

 ten years. Tlie number Dr. Collett has col- 

 lected data for is surprising. He gives the 

 dates and areas invaded for seven great 

 migrations from IT-iD to 1790. and for no 

 less than 24 in the present century. 



As to the extent of the areas invaded. Dr. 

 Collett says : '"On the whole it may be as- 

 sumed that scarcely any accessible point of 

 Xorway (except the outermost islets) has 

 not been iuvadt'd b^- their hordes during 

 one or other prolific year." 



" It has hardly ever happened that a pro- 

 lific year (and the con.sequeiit migration) 

 has simultaneously embraced the eutu-e 

 land. The rule is that the increase takes 

 place in great or small districts independent 

 of each other, but the area which may be 

 involved thereby may be of very consider- 

 able extent. Occasionally the increase will 

 take place simultaneously in two separate 

 districts, divided from each other by an 

 area of greater or lesser extent, in which 

 the production is normal. In Xorway there 

 nuiy be recognized, on the whole, at least five 

 great groups of mountains within which 

 most of the migrations have their radiating 

 centre. One migration may embrace either 

 the entire group or small portions of it." 



The regular enemies of the Lemming are 

 numerous and many of them increase with 

 the Lemmings : as the birds of prej% the 

 large gulls and skuas, and weasels and 

 foxes. In prolific years certain birds which 

 follow the Lemmings change their breeding 

 grounds and nest in localities where they 

 are never seen at other times. To these 

 may be added certain irregular enemies; 

 for Dr. Collett tells us that reindeer (Iwth 

 wild and domesticated), cows, goats and 

 pigs kill and eat them in great numbers. 



