[10] Still more remarkable is the increase of rabbits both in New Zealand and Australia. No less than seven millions of rabbit-skins have been exported from the former country in a single year, their value being £67,000. In both countries, sheep-runs have been greatly deteriorated in value by the abundance of rabbits, which destroy the herbage; and in some cases they have had to be abandoned altogether.
[11] Later observers have proved that two eggs are laid and usually two young produced, but it may be that in most cases only one of these comes to maturity.
[12] Origin of Species, p. 59. Professor A. Newton, however, informs me that these species do not interfere with one another in the way here stated.
[13] Winwood Reade's Martyrdom of Man, p. 520.
[14] Nineteenth Century, February 1888, pp. 162, 163.
[15] The Kestrel, which usually feeds on mice, birds, and frogs, sometimes stays its hunger with earthworms, as do some of the American buzzards. The Honey-buzzard sometimes eats not only earthworms and slugs, but even corn; and the Buteo borealis of North America, whose usual food is small mammals and birds, sometimes eats crayfish.
CHAPTER III
THE VARIABILITY OF SPECIES IN A STATE OF NATURE
Importance of variability—Popular ideas regarding it—Variability of the lower animals—The variability of insects—Variation among lizards—Variation among birds—Diagrams of bird-variation—Number of varying individuals—Variation in the mammalia—Variation in internal organs—Variations in the skull—Variations in the habits of Animals—The Variability of plants—Species which vary little—Concluding remarks.