which to explain the metamorphoses which, as I also believe, have
occurred."

Here again we must venture to dissent completely from Professor
Kolliker's conception of Mr. Darwin's hypothesis. It appears to us to
be one of the many peculiar merits of that hypothesis that it involves
no belief in a necessary and continual progress of organisms.

Again, Mr. Darwin, if we read him aright, assumes no special tendency
of organisms to give rise to useful varieties, and knows nothing of
needs of development, or necessity of perfection. What he says is, in
substance: All organisms vary. It is in the highest degree improbable
that any given variety should have exactly the same relations to
surrounding conditions as the parent stock. In that case it is either
better fitted (when the variation may be called useful), or worse
fitted, to cope with them. If better, it will tend to supplant the
parent stock; if worse, it will tend to be extinguished by the parent
stock.

If (as is hardly conceivable) the new variety is so perfectly adapted to
the conditions that no improvement upon it is possible,--it will
persist, because, though it does not cease to vary, the varieties will
be inferior to itself.

If, as is more probable, the new variety is by no means perfectly
adapted to its conditions, but only fairly well adapted to them, it
will persist, so long as none of the varieties which it throws off are
better adapted than itself.

On the other hand, as soon as it varies in a useful way, i.e. when the