| → other parasitic insects. 1861 1866 1869 1872 |
| birds. 1859 1860 |
|
| → OMIT 1861 1866 1869 1872 |
| (whose numbers are probably regulated by hawks or beasts of prey) 1859 1860 |
|
| → 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 |
|
| → 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 |
|
| → uniform for long periods of time, 1859 1860 1861 1866 1869 |
| for long periods of time uniform, 1872 |
|
|
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. Hence, if certain insectivorous birds
→OMIT
were to
in Paraguay, the
→parasitic insects would probably increase;
and this would
→lessen the number of the navel-frequenting flies—then cattle and horses would become feral, and this would certainly
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
seen in
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
nature the relations
ever be as simple as this. Battle within battle must
be
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,
though assuredly the merest trifle would
give the victory to one organic being over another.
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! |
|
| I am tempted to give one more instance showing how plants and animals,
remote in the scale of nature,
|
