world insects determine the existence of cattle. Perhaps Paraguay offers the most curious instance of this; for here neither cattle nor horses nor dogs have ever run wild, though they swarm southward and northward in a feral state; and Azara and Rengger have shown that this is caused by the greater number in Paraguay of a certain fly, which lays its eggs in the navels of these animals when first born. The increase of these flies, numerous as they are, must be habitually checked by some means, probably by
other parasitic insects. other parasitic insects. 1861 1866 1869 1872 |
birds. 1859 1860 |
Hence, if certain insectivorous birds
...OMIT 1861 1866 1869 1872 |
(whose numbers are probably regulated by hawks or beasts of prey) 1859 1860 |
were to
decrease decrease 1861 1866 1869 1872 | increase 1859 1860 |
in Paraguay, the
parasitic insects would probably increase; parasitic insects would probably increase; 1861 1866 1869 1872 |
flies would decrease— then cattle and horses would become feral, 1859 |
flies would decrease— then cattle and horses would became feral, 1860 |
and this would
lessen the number of the navel-frequenting flies—then cattle and horses would become feral, and this would certainly lessen the number of the navel-frequenting flies—then cattle and horses would become feral, and this would certainly 1869 |
certainly 1859 1860 |
lessen the number of the navel-frequenting flies— then cattle and horses would become feral, and this would certainly 1861 1866 1872 |
greatly alter (as indeed I have observed in parts of South America) the vegetation: this again would largely affect the insects; and this, as we
have just have just 1861 1866 1869 1872 | just have 1859 1860 |
seen in
Staffordshire, Staffordshire, 1859 1861 1866 1869 1872 | Stafford-shire, 1860 |
the insectivorous birds, and so onwards in ever-increasing circles of complexity. We began this series by insectivorous birds, and we have ended with them. Not that
in in 1859 1860 1861 1866 1869 | under 1872 |
nature the relations
can can 1859 1860 1861 1866 1869 | will 1872 |
ever be as simple as this. Battle within battle must
ever ever 1859 1860 1861 1866 1869 | ever 1872 |
be
recurring recurring 1859 1860 1861 1866 1869 | continually recurring 1872 |
with varying success; and yet in the long-run the forces are so nicely balanced, that the face of nature remains
uniform for long periods of time, uniform for long periods of time, 1859 1860 1861 1866 1869 |
for long periods of time uniform, 1872 |
though assuredly the merest trifle would
often often 1859 1860 1861 1866 1869 | often 1872 |
give the victory to one organic being over another.
Nevertheless, Nevertheless, 1861 1866 1869 1872 | Nevertheless 1859 1860 |
so profound is our ignorance, and so high our presumption, that we marvel when we hear of the extinction of an organic being; and as we do not see the cause, we invoke cataclysms to desolate the world, or invent laws on the duration of the forms of life! |