1895.] MYODES LEMMUS. 35 

5. The extensive mountain plateaux of Finmarken (and the 
large islands), whence the valleys and lowlands ot Fin- 
marken are invaded in all directions. 
Each of the great migrations will, as å rule, originate 
in one of these chief centres. In some years migrations may 
take place simultaneously from several of them; thus those of 
Nos 1 and 2, or 8 and 4, may often have migratory years at 
the same time. 
The 3rd centre may be pointed out as å district which ap- 
pears to be specially favoured by these prolific years. In no 
other portions of the country do the migrations appear to have 
occurred so frequently as in those around the Trondhjems Fjord. 
The minor exodus'es may, as we have previously mentioned, 
only include a few of the adjacent valleys which radiate from 
a joint plateau. 
In like manner å prolific year may occur on å cluster of 
islands, whilst such cannot be traced on the adjacent mainland. 
This is, for instance, the case in respect to several of the large 
islands off the coasts of Tromse. On each of these islands å 
migration may thus take place during the autumn down to the 
shore; and in such years, on even quite insignificant islets, 
where in ordinary years their presence has hardly been suspected, 
the lemmings may be suddenly observed to appear in swarms. 
10. The Direction and Extent of the Migrations. 

The directiom of the march 18, invartably, mainly dependent 
on the valleys, so that the exodus cam radiate in quite opposite 
directions from one and the same mountain plateau. 
Thus, during migratory years, the southern ramifications of 
the Lang Fjeld will emit swarms which may advance eastward, 
as far as the Christiania Fjord; southward, down to the coastal 
regions of Christiansand Stift; and westwards, to the Fjords in 
