imitive 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.

Thus I have no doubt that Mr. Darwin's hypothesis will be found
competent to explain the majority of the phenomena exhibited by species
in nature; but in an earlier lecture I spoke cautiously with respect to
its power of explaining all the physiological peculiarities of species.

There is, in fact, one set of these peculiarities which the theory of
selective modification, as it stands at present, is not wholly competent
to explain, and that is the group of phenomena which I mentioned to you
under the name of Hybridism, and which I explained to consist in the
sterility of the offspring of certain species when crossed one with
another. It matters not one whit whether this sterility is universal,
or whether it exists only in a single case. Every hypothesis is bound
to explain, or, at any rate, not be inconsistent with, the whole of the
facts which it professes to account for; and if there is a single one of
these facts which can be shown to be inconsistent with (I do not merely
mean inexplicable by, but contrary to) the hypothesis, the hypothesis
falls to the ground,--it is worth nothing. One fact with which it is
positively inconsistent is worth as much, and as powerful in negati