ld have been
highly abnormal in comparison with all their congeners. They maintain that
certain species, which formerly existed, have become extinct or unknown,
although the world is now so much better known. The assumption of so much
recent extinction is no difficulty in their eyes; for they do not judge of
its probability by the facility or difficulty of the extinction of other
closely allied wild forms. Lastly, {408} they often ignore the whole
subject of geographical distribution as completely as if its laws were the
result of chance.

Although from the reasons just assigned it is often difficult to judge
accurately of the amount of change which our domesticated productions have
undergone, yet this can be ascertained in the cases in which we know that
all the breeds are descended from a single species, as with the pigeon,
duck, rabbit, and almost certainly with the fowl; and by the aid of analogy
this is to a certain extent possible in the case of animals descended from
several wild stocks. It is impossible to read the details given in the
earlier chapters, and in many published works, or to visit our various
exhibitions, without being deeply impressed with the extreme variability of
our domesticated animals and cultivated plants. I have in many instances
purposely given details on new and strange peculiarities which have arisen.
No part of the organisation escapes the tendency to vary. The variations
generally affect parts of small vital or physiological importance, but so
it is with the differences which exist between closely allied species. In
these unimportant characters there is often a greater difference between
the breeds of the same species than between the natural species of the same
genus, as Isidore Geoffroy has shown to be the case with size, and as is
often the case with the colour, texture, form, &c., of the hair, feathers,
horns, and other dermal appendages.

It has often been asserted that important parts never vary under
domestication, but this is a complete error. Look at the skull of the pig
in any one of the highly improved breeds, with the occipital condyles and
other parts greatly modified; or look at that of the niata ox. Or again, in
the several breeds of the rabbit, observe the elongated skull, with the
differently shaped occipital foramen, atlas, and other cervical vertebrae.
The whole shape of the brain, together with the skull, has been modified in
Polish fowls; in other breeds of the fow