external conditions of life, as climate and food, etc., seem to have
induced some slight modifications. Habit, in producing constitutional
differences, and use, in strengthening, and disuse, in weakening and
diminishing organs, seem to have been more potent in their effects."

And finally, as if to prevent all possible misconception, Mr. Darwin
concludes his Chapter on Variation with these pregnant words:--

"Whatever the cause may be of each slight difference in the offspring
from their parents--and a cause for each must exist--it is the steady
accumulation, through natural selection of such differences, when
beneficial to the individual, that gives rise to all the more important
modifications of structure which the innumerable beings on the face of
the earth are enabled to struggle with each other, and the best adapted
to survive."

We have dwelt at length upon this subject, because of its great general
importance, and because we believe that Professor Kolliker's criticisms
on this head are based upon a misapprehension of Mr. Darwin's
views--substantially they appear to us to coincide with his own. The
other objections which Professor Kolliker enumerates and discusses are
the following*:--

[footnote] *Space will not allow us to give Professor
Kolliker's arguments in detail; our readers will find a
full and accurate version of them in the 'Reader' for
August 13th and 20th, 1864.

"1. No transitional forms between existing species are known; and known
varieties, whether selected or spontaneous, never go so far as to