heless, though our ducks and geese, for example, are
of the same type as their wild progenitors, they have lost the power of
long and sustained flight, and have become in other respects
considerably modified.[281]

"A bird, after having been kept five or six years in a cage, cannot on
being liberated fly like its brethren which have been always free. Such
a change in a single lifetime has not effected any transmissible
modification of type; but captivity, continued during many successive
generations, would undoubtedly do so. If to the effects of captivity
there be added also those of changed climate, changed food, and changed
actions for the purpose of laying hold of food, these, united together
and become constant, would in the course of time develop an entirely new
breed."

This, again, is almost identical with the passage from Buffon,[282] p.
148 of this volume. See also pp. 169, 170.

"Where can our many domestic breeds of dogs be found in a wild state?
Where are our bulldogs, greyhounds, spaniels, and lapdogs, breeds
presenting differences which, in wild animals, would be certainly called
specific? These are all descended from an animal nearly allied to the
wolf, if not from the wolf itself. Such an animal was domesticated by
early man, taken at successive intervals into widely different climates,
trained to different habits, carried by man in his migrations as a
precious capital into the most distant countries, and crossed from time
to time with other breeds which had been developed in similar ways.
Hence our present multiform breeds."[283]

Here, also, it is impossible to forget Buffon's passages on the dog,
given pp. 121, 122. See also p. 223.

"Observe the gradations which are found between the _ranunculus
aquatilis_ and the _ranunculus hederaceus_: the latter--a land
plant--resembles those parts of the former which grow above the surface
of the water, but not those that grow beneath it.[284]

"The modifications of animals arise more slowly than those of plants;
they are therefore less easily watched, and less easily assignable to
their true causes, but they arise none the less surely. As regards these
causes, the most potent is diversity of the surroundings in which they
exist, but there are also many others.[285]

"The climate of the same place changes, and the place itself changes
with changed climate and exposure, but so slowly that we imagine all
lands to be stable in their conditions. This, howeve