95 
on the constitution, and impel beings of different 
classes to temporary changes of condition and lo- 
cality. 
Amongst the mammalia of northern regions some 
are impelled to migrate during the severity of the 
long winter, by the total disappearance of all vege- 
tation. ‘The musk-ox and reindeer deserted Mel- 
ville Island and the northern shores of the arctic 
sea, and fled southward from the rigours of the nine 
months winter, leaving captain Parry and the other 
officers, and the crews of the Hecla and Griper, 
nearly the sole living and moving beings within the 
seventy-fourth degree of north latitude. 
In the months of June, July, and August, the 
deer are driven by the gad-fly, cestrus tarandi, from 
the valleys of Lapland to the lofty and snowy regions 
of the mountains, where the cold is fatal to their 
tormentor. This, no doubt, with other insects, co- 
operating probably with other impelling causes, drives 
the herds, which had left the arctic circle during 
the winter, back again during the summer months. 
As my excellent and accomplished brother has 
given already a synopsis of the leading facts rela- 
tive to migration in his Lecture on that subject, 
read in the Ashmolean Museum, and published at 
Oxford; I shall only observe, that amongst mam- 
malia, the most remarkable migrators, are the lem- 
ming rats or mice of Lapland, Sweden, and Nor- 
way, which are said to march in swarms of congre- 
gated millions, leaving barrenness and famine to 
