all the forms of Dogs, Wolves, and Foxes from a common
ancestor.

Again, it is objected that the Pouter or the Fan-tail pigeon cannot be
further developed in the same direction. Variation seems to have reached
its limits in these birds. But so it has in nature. The Fan-tail has not
only more tail feathers than any of the three hundred and forty existing
species of pigeons, but more than any of the eight thousand known
species of birds. There is, of course, some limit to the number of
feathers of which a tail useful for flight can consist, and in the
Fan-tail we have probably reached that limit. Many birds have the
oesophagus or the skin of the neck more or less dilatable, but in no
known bird is it so dilatable as in the Pouter pigeon. Here again the
possible limit, compatible with a healthy existence, has probably been
reached. In like manner the differences in the size and form of the beak
in the various breeds of the domestic Pigeon, is greater than that
between the extreme forms of beak in the various genera and sub-families
of the whole Pigeon tribe. From these facts, and many others of the same
nature, we may fairly infer, that if rigid selection were applied to any
organ, we could in a comparatively short time produce a much greater
amount of change than that which occurs between species and species in a
state of nature, since the differences which we do produce are often
comparable with those which exist between distinct genera or distinct
families. The facts adduced by the writer of the article referred to, of
the definite limits to variability in certain directions in domesticated
animals, are, therefore, no objection whatever to the view, that all the
modifications which exist in nature have been produced by the
accumulation, by natural selection, of small and useful variations,
since those very modifications have equally definite and very similar
limits.

_Objection to the Argument from Classification._

To another of this writer's objections--that by Professor Thomson's
calculations the sun can only have existed in a solid state 500,000,000
of years, and that therefore _time_ would not suffice for the slow
process of development of all living organisms--it is hardly necessary
to reply, as it cannot be seriously contended, even if this calculation
has claims to approximate accuracy, that the process of change and
development may not have been sufficiently rapid to have occurred within
that period. His