as implying the summation of small differences. Professor Henslow
in his _Heredity of Acquired Characters in Plants_, 1908, p. 2,
quotes from Darwin's _Var. under Dom._, Ed. i. II. p. 271, a
passage in which the author, speaking of the direct action of
conditions, says:--"A new sub-variety would thus be produced
without the aid of selection." Darwin certainly did not mean to
imply that such varieties are freed from the action of natural
selection, but merely that a new form may appear without
_summation_ of new characters. Professor Henslow is apparently
unaware that the above passage is omitted in the second edition of
_Var. under Dom._, II. p. 260.

Even in well-established breeds the individuals of which to an
unpractised eye would appear absolutely similar, which would give, it
might have been thought, no scope to selection, the whole appearance of
the animal has been changed in a few years (as in the case of Lord
Western's sheep), so that practised agriculturalists could scarcely
credit that a change had not been effected by a cross with other breeds.
Breeders both of plants and animals frequently give their means of
selection greater scope, by crossing different breeds and selecting the
offspring; but we shall have to recur to this subject again.

The external conditions will doubtless influence and modify the results
of the most careful selection; it has been found impossible to prevent
certain breeds of cattle from degenerating on mountain pastures; it
would probably be impossible to keep the plumage of the wild-duck in the
domesticated race; in certain soils, no care has been sufficient to
raise cauliflower seed true to its character; and so in many other
cases. But with patience it is wonderful what man has effected. He has
selected and therefore in one sense made one breed of horses to race and
another to pull; he has made sheep with fleeces good for carpets and
other sheep good for broadcloth; he has, in the same sense, made one dog
to find game and give him notice when found, and another dog to fetch
him the game when killed; he has made by selection the fat to lie mixed
with the meat in one breed and in another to accumulate in the bowels
for the tallow-chandler{199}; he has made the legs of one breed of
pigeons long, and the beak of another so short, that it can hardly feed
itself; he has previously determined how the feathers on a bird's body
shall be c