fowl in three; those of the duck in four; those of the goose in five;
and those of the ostrich in seven weeks. As far as we can judge, a
recurrent period, if approximately of the right duration for any
process or function, would not, when once gained, be liable to change;
consequently it might be thus transmitted through almost any number of
generations. But if the function changed, the period would have to
change, and would be apt to change almost abruptly by a whole week.
This conclusion, if sound, is highly remarkable; for the period of
gestation in each mammal, and the hatching of each bird s eggs, and
many other vital processes, thus betray to us the primordial birthplace
of these animals.), resembling the larvae of existing Ascidians. These
animals probably gave rise to a group of fishes, as lowly organised as
the lancelet; and from these the Ganoids, and other fishes like the
Lepidosiren, must have been developed. From such fish a very small
advance would carry us on to the Amphibians. We have seen that birds
and reptiles were once intimately connected together; and the
Monotremata now connect mammals with reptiles in a slight degree. But
no one can at present say by what line of descent the three higher and
related classes, namely, mammals, birds, and reptiles, were derived
from the two lower vertebrate classes, namely, amphibians and fishes.
In the class of mammals the steps are not difficult to conceive which
led from the ancient Monotremata to the ancient Marsupials; and from
these to the early progenitors of the placental mammals. We may thus
ascend to the Lemuridae; and the interval is not very wide from these
to the Simiadae. The Simiadae then branched off into two great stems,
the New World and Old World monkeys; and from the latter, at a remote
period, Man, the wonder and glory of the Universe, proceeded.
Thus we have given to man a pedigree of prodigious length, but not, it
may be said, of noble quality. The world, it has often been remarked,
appears as if it had long been preparing for the advent of man: and
this, in one sense is strictly true, for he owes his birth to a long
line of progenitors. If any single link in this chain had never
existed, man would not have been exactly what he now is. Unless we
wilfully close our eyes, we may, with our present knowledge,
approximately recognise our parentage; nor need we feel ashamed of it.
The most humble organism is something much higher than the inorganic
dust under our feet; and no one with an unbiassed mind can study any
living creature, however humble, without being struck with enthusiasm
at its marvellous structure and properties.
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