96 
mark the direction of their destructive course : much 
resembling those northern hordes of human beings 
in numbers and ferocity, the acknowledged ances- 
tors of the greater part of the population of Europe, 
who trampled down the arts of Greece, and the 
splendour and the power of ancient Rome. The 
mus ceconomicus, or Kamtschatka rat, is said to 
rival the lemmings in its armies of migration. Ex- 
cess of population seems with these animals to be 
the impelling cause of migration. Squirrels are also 
said to migrate from the same cause, and even to 
make long voyages on pieces of pine and birch bark. 
See Bingley, vol. i. p. 392. and his references. Some, 
however, of either genus do not migrate. The wolf 
and fox appear to prowl abroad during the utmost 
severity of the arctic winter. The wolf was at- 
tracted by the odours from the ships in Melville har- 
bour, long after the total disappearance of all other 
animals. 
It is notorious that while swallows, blackcaps, 
redstarts, &c. regularly leave Britain on the approach 
of winter, the robin, the wren, and even the little 
golden-crowned wren, remain during our most severe 
seasons. Of pigeons, some remain with us, as the 
stock-dove; some migrate, as the ring-dove. The 
columba migratoria of North America is only to be 
compared in respect to vastness of the migratory 
multitude, and to the destruction attending their 
visits wherever they alight, to the lemmings amongst 
quadrupeds. Land-crabs migrate among crustacea; 
