als have certainly ceased
to exist since man inhabited the globe. There have been, doubtless, many
others that have shared the same fate, which we know nothing about. It
is only within the last hundred years that we have had anything
approaching to an acquaintance with the living fauna of the earth; yet,
during that time some seven or eight creatures we know have been
extinguished. Fully half of these,--the Auk, the Didunculus, the
Notornis, and the Nestor,--within the last ten years! It would really
seem as if the more complete and comprehensive an acquaintance with the
animals of the world became, the more frequently this strange phenomenon
of expiring species was presented to us. Perhaps it is not extravagant
to suppose that--including all the invertebrate animals, the countless
hosts of insects, and all the recondite forms that dwell in the recesses
of the ocean--a species fades from existence every year. All the
examples that have been given were either Mammalia or Birds, (_the
Colossochelys_ only excepted:) now these, though the most conspicuous
and best known, are almost the least populous classes of living beings.
There is no reason whatever for concluding that the law of mortality of
species does not extend to all the other classes, vertebrate and
invertebrate, in an equal ratio, so that my estimate will appear, I
think, a very moderate one. Yet it is a startling thought, and one which
the mind does not entertain without a measure of revulsion, that the
passing of every century in the world's history has left its fauna
_minus_ a hundred species of animals that were denizens of the earth
when it began. I was going to say "left the fauna so much _poorer_;" but
that I am not sure of. The term would imply that the blanks are not
filled up; and that, I repeat, I am not sure of. Probability would
suggest that new forms are continually created to supply the lack of
deceased ones; and it may be that _some_, at least, of the creatures
ever and anon described as new to science, especially in old and
well-searched regions, may be newly called into being, as well as newly
discovered. It may be so, I say; I have no evidence that it is so,
except the probability of analogy; we know that the rate of mortality
among _individuals_ of a species, speaking generally, is equalled by the
rate of birth, and we may suppose this balance of life to be paralleled
when the unit is a species, and not an individual. If the Word of God
contai