1895.| MYODES LEMMUS. 23 


Since 1862, I have, personally, on several occasions, been 
enabled to observe the lemming during its prolific and migratory 
years in Norway. In 1863, all the mountains of Gudbrands- 
dalen and Dovre were covered with their hordes, and an impo- 
sing emigration took place to the southerly lowlands as far down 
as the Christiania Fjord. At the same time Å. ratticeps (and 
possibly yet another Arvicola) increased in multitudes in the 
same distriets; game-birds were exceptionally numerous, and the 
larvæ of Cidaria dilutata devastated great tracts of the birch 
forests. 
In Aaseral (Christiansand Stift), where there was the same 
year likewise an abnormal increase of the lemming, A. amphibtus, 
and one or two other (undefined) species of Arvicola were simul- 
taneously numerous, besides Mus sylvaticus. 
In 1872, another abnormal increase of M. lemmus took 
place in the southern mountain districts. Other species likewise 
appeared simultaneously in great numbers, such as Sorex ara- 
neus. When I, the same summer, visited Tromsö and West 
Finmark, I found M. lemmus to be rather scarce there, whilst 
other species, quite independent of the lemming, had there å 
very prolifie year. Cannabina limaria and Fringilla montifringilla 
thus appeared everywhere throughout the birch forests in such 
enormous numbers, and bred, it may be said, *in every bush,” 
that I have never since seen anything like it. 
Similar examples may be brought forward from all subse- 
quent lemming years. In 1883, when this species migrated 
in Saltdalen near Bodö, A. glareolus and Å. gregarius likewise 
appeared in such great numbers that they (especially the former 
species) became å plague to the country!; at the same time 
the year was particularly favourable to the development of Te- 
trao urogallus, and T. tetrix, as well as the two species Lagopus. 
Likewise in 1890, when Myodes had å (less) prolific year 
in the Österdal mountains, the year was unexceptionally favour- 
1 See Hagemann, *Gnaverne i sit Forhold til Furuskoven*%. (Den 
Norske Forstforenings Aarbog for 1889, p. 26). 
