was Professor at Oxford and a Fellow of the Royal Society, and who
maintained that _Zoaea_ was a mature and independent form. In the end
taxonomy had to be altered so as to conform with the fact of development,
and the name _Zoaea_ disappeared altogether as that of an independent
genus, persisting only as a convenient term for an important larval stage
in the development of crabs.

These two kinds of study give us a knowledge of the animals now living.
But we find it a universal rule that the individual animal is transitory,
that the duration of life, though varying from a few weeks to more than a
century, is limited, and that new individuals arise by reproduction, and
we have no evidence that the series of successive generations has ever
been interrupted; that is to say, the series in any given individual or
species may come to an end; species may be exterminated, but we know of no
instance of individuals coming into existence except by the process of
reproduction or generation from pre-existing individuals. Further, we know
from the evidence of fossil remains that the animals existing in former
periods were very different from those existing now, and that many of the
existing forms, such as man, mammals, birds, bony fishes, can only be
traced back in the succession of stratified rocks to the later strata or
to those about the middle of the series, evidence of their existence in
the periods represented by the most ancient strata being entirely absent.
Existing types then must have arisen by evolution, by changes occurring in
the succession of generations.

These three facts--namely, the limited duration of individual life, the
uninterrupted succession of generations, and the differences of the
existing animals and plants from those of former geological periods whose
remains are preserved in stratified rocks--are sufficient by themselves to
prove that evolution has taken place, that the history of organisms has