
Se 
30 er R. COLLETT. - oe 
Arvicola ratticeps. As I have above mentioned, this excep- 4 
tional productiveness in M. lemmus is nothing peculiar to this 
species, as the same phenomena recur in other kindred species. 
I shall here add a few observations which I made at the 
same time (during the same stay at Gausdal) in 1891, concerning 
the breeding conditions of A. ratticeps, å Species which, with us, 
is mostly sub-alpine in its occurence, as it inhabits the grassy 
spots on the sides of the mountain plateaux!. 
In the mountains about the Gudbrandsdal, the year men- 
tioned was åa prolific one for this species as well as for M. lem- 
mus, and the two species were constantly running about in 
the paths, beaten by both in the grass. 
The bulk of the individuals, in August that year, consisted 
of young of the first litter, which in size were about the same 
as the old ones, and also non-matured young of the second and 
third litters. But comparatively few specimens of the old stock 
(from the previous year) were still to be seen. As å rule these 
had just produced their third litter in the nest, but many too 
were pregnant (with the fourth set). 
At the same time their offspring of the first litter were 
also in young, or had milk in their teats (young in the nest). 
Qne yearling which I examined on the 24th August, had 
milk in its teats, and must therefore be presumed to have had 
young in the nest; but it was besides pregnant with not fully 
developed embryos (possibly the second litter); and several nests, 
which towards the end of August I still found in the course of 
verschiedenen Jahren auf ganz gleiche Weise vor sich geht, dass aber 
die Anzahl der am Leben bleibenden jungen Lemminge in der un- 
ginstigen Jahren sehr gering ist, wåhrend sie in der giinstigen eine 
massenweise Anhailfung der Individuen bewirken kann.” (Pleske, 
Lien: 99) 
! A. ratticeps, Keys. and Blas., has, in Norway, about the same lati- 
tudinal range as M. lemmus, as it appears from the southernmost 
mountains of the country up to Finmarken. lt is, however, on the 
whole far more confined in its habitat, as it only occupies the nar- 
row borders of the mountain sides which adjoin the true uplands, 
but only in small numbers the plateaux themselves. It appears, be- 
sides, to be more localized in its occurrence. 
