46 R. COLLETT. 
exposed to their depredations, the barley fields to a lesser ex- 
tent; and the damage which they, while wintering, do the hay 
or grain stored in barns or outhouses, may be very considerable. 
Man does not reap any appreciable benefit from them. 
Their coats, notwithstanding their beautiful markings, prove to 
be of hardly of any service. 

15. Enemies. 
How are the numbers of the superfiuous individuals reduced 
to the normal, and how do the migrations cease? 
All those that reach the lowlands during their wanderings 
die in exile, and none ever return alive. 
Men kill them whenever they have å chance; but human 
interference has, however, but little effect on the masses.  Nume- 
rous enemies amongst animals work unceasingly for their exier- 
mination, and this is of greater consequence. Thousands perish 
from accidents of every kind, and this continually assists in re- 
ducing their numbers. But the most active factor wm their ex- 
terminaltion appears to be infectious diseases, which invariably 
oceur whenever a species of animal has multiplied in excess of its 
natural numbers. 
The number of their enemies corresponds on the whole to 
their own great increase. We have previously mentioned the 
kinds of rapacious birds, and beasts of prey which, in ordinary 
years, derive their daily sustenance from the ranks of the lem- 
mings. During prolific years the numbers of their enemies in- 
crease, as Various ether species immigrate to the spot, multiply 
greatly, like the lemmings themselves, and kill them daily im 
great masses. Amongst the more or less ordinary feeders on 
lemmings which, during migratory years on-the mountain plateaux, 
or the sub-alpine parts, live more or less exclusively on them, 
may be named (with us in Norway) Gulo luscus, Camis vulpes 
Å 
[No. 54 



