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were spreading everywhere, the latter displacing the native grasses, 
and the watercress was choking the streams, much in the same way as 
the American pond weed Awacharis was choking our English rivers. 
There did not seem the same vital force in plants imported from the 
Southern Hemisphere to the Northern, as from the Northern to the 
Southern ; some of our Northern plants, it was said, which seeded 
with us but once a year, or were only annuals, seeded frequently, or 
became biennials or perennials. 
Buffon started the doctrine, that “taking beings generally, the 
total quantity of life is always the same,” and “that man has made 
choice of some twenty species of birds and mammals, and these 
twenty species figure more largely in Nature, and are of more advantage 
to the world than all the others put together.” Flourens, arguing from 
Buffon’s dicfa, has shewn that this tendency had always been 
observable—“ relatively to the quantity of life, there is a kind of 
compensation upon the globe—in proportion as certain species die out 
the number of individuals in some others increases.” And Darwin 
and his followers had shewn how, in the struggle for existence, the 
more powerful, and those best able to accommodate themselves to 
altered circumstances, survived, while the weaker and less yielding, 
had become extirpated. 
Looking first at man and his selected mammals, and those animals 
which followed his footsteps, they had driven out, and were still driving 
out, the noxious and injurious animals, and replacing them with the 
useful. It was quite true that some of his companions did become 
pests. There was a Maori saying, ‘‘ As the white man’s rat has driven 
away the native rat, as the European fly drives away our own, and the 
clover kills our fern, so will the Maoris disappear before the white 
man himself”—a prophecy which it was feared, judging from the past 
history of the world, was too likely to be fulfilled. It was perfectly true 
that the Norwegian rat, which had nearly in our own island extirpated 
the black rat, had in parts of New Zealand extirpated the native rat, 
itself in many cases going out before the European mouse, while so 
patent was the disappearance of the native blue-bottle before the 
house-fly that colonists, knowing its usefulness, carried it with them 
in boxes or bottles to the inland stations. The pig, too, had become such 
a pest, that when 6d. a tail was offered, 22,000 tails were brought in from 
some runs without an apparent diminution in their numbers. 
Descending to a still lower level, we saw how the balance of life 
