has yet been advanced. It is one remarkable peculiarity of Mr.
Darwin's hypothesis that it involves no necessary progression or
incessant modification, and that it is perfectly consistent with the
persistence for any length of time of a given primitive stock,
contemporaneously with its modifications. To return to the case of the
domestic breeds of pigeons, for example; you have the Dove-cot pigeon,
which closely resembles the Rock pigeon, from which they all started,
existing at the same time with the others. And if species are
developed in the same way in nature, a primitive stock and its
modifications may, occasionally, all find the conditions fitted for
their existence; and though they come into competition, to a certain
extent, with one another, the derivative species may not necessarily
extirpate the primitive one, or 'vice versa'.

Now palaeontology shows us many facts which are perfectly harmonious
with these observed effects of the process by which Mr. Darwin supposes
species to have originated, but which appear to me to be totally
inconsistent with any other hypothesis which has been proposed. There
are some groups of animals and plants, in the fossil world, which have
been said to belong to "persistent types," because they have persisted,
with very little change indeed, through a very great range of time,
while everything about them has changed largely. There are families of
fishes whose type of construction has persisted all the way from the
carboniferous rock right up to the cretaceous; and others which have
lasted through almost the whole range of the secondary rocks, and from
the lias to the older tertiaries. It is something stupendous this--to
consider a genus lasting without essential modifications through all
this enormous lapse of time while almost everything else was changed
and modified.