ON THE DISTRIBUTION OF MAMMALIA IN EUROPE. 215 
But the exact number of mammals to be found within the 
political limits of the Continent of Europe is to a great 
extent determined by the systematist’s penchant for differen- 
tiation. Keyserling and Blasius recognise 149 species in 56 
genera, but in this list are included some species which have 
been imported from distant regions, others which can only 
be regarded as stragglers from the conterminous parts of 
Asia, and others again whose claim to segregation is by no 
means universally admitted. Even if all questionable cases 
be subtracted, the number, small as it may appear, is in 
reality large in proportion to the conditions implied by the 
habitat ; for here the struggle for existence has been more 
vehemently maintained than in any other quarter of the 
world. In density of population, Europe, with 38 inhabitants 
to the square kilometre, far surpasses all the other continents. 
Asia, which ranks next to it in this respect, has only 18 or 
19; Africa is supposed to have about 5; America has barely 
3, and Oceania not even 1. And this difference becomes 
more conspicuous when the political divisions of each con- 
tinent are separately considered ; for within the states of 
Western and Central Europe is compressed a sixth part of 
the entire population of the earth. Of these, Belgium con- 
tains 218 inhabitants to the square kilometre, Great Britain 
120, Italy 109, Germany 100. The United States of America, 
the one civilized country which can be brought into com- 
parison with Europe in this connection, has scarcely 8. The 
great Empire State, New York, has not the population of 
Belgium though its area is more than four times as large; 
and if Rhode Island and Massachusetts, with a density of 
106 and 104 respectively, rank with the most thickly-peopled 
parts of our continent, there are, on the other hand, states 
and territories in the Far West in comparison with which 
even Norway, the poorest country in Europe, would present 
a crowded aspect. Within the present century the popula- 
tion of almost all the European States has greatly increased. 
In 1801 England had only 9 million inhabitants; in 1851 
the number was found to have doubled; in 1891 it had 
increased to nearly 314 millions. The progress of Germany 
has been even more remarkable. Not only in these prosper- 
ous countries, but in France and Spain, where the growth of 
