a page is done with: and
secondly the ordinary erasures by horizontal lines. I have not been
quite consistent in regard to these: I began with the intention of
printing (in square brackets) all such erasures. But I ultimately found
that the confusion introduced into the already obscure sentences was
greater than any possible gain; and many such erasures are altogether
omitted. In the same way I have occasionally omitted hopelessly obscure
and incomprehensible fragments, which if printed would only have
burthened the text with a string of <illegible>s and queried words. Nor have I
printed the whole of what is written on the backs of the pages, where it
seemed to me that nothing but unnecessary repetition would have been the
result.

In the matter of punctuation I have given myself a free hand. I may no
doubt have misinterpreted the author's meaning in so doing, but without
such punctuation, the number of repellantly crabbed sentences would have
been even greater than at present. In dealing with the Essay of 1844, I
have corrected some obvious slips without indicating such alterations,
because the MS. being legible, there is no danger of changing the
author's meaning.

The sections into which the Essay of 1842 is divided are in the original
merely indicated by a gap in the MS. or by a line drawn across the page.
No titles are given except in the case of Sec. VIII.; and Sec. II. is the only
section which has a number in the original. I might equally well have
made sections of what are now subsections, _e.g. Natural Selection_ p.
7, or _Extermination_ p. 28. But since the present sketch is the germ of
the Essay of 1844, it seemed best to preserve the identity between the
two works, by using such of the author's divisions as correspond to the
chapters of the enlarged version of 1844. The geological discussion with
which Part II begins corresponds to two chapters (IV and V) of the 1844
Essay. I have therefore described it as Sec.Sec. IV. and V., although I cannot
make sure of its having originally consisted of two sections. With this
exception the ten sections of the Essay of 1842 correspond to the ten
chapters of that of 1844.

The _Origin of Species_ differs from the sketch of 1842 in not being
divided into two parts. But the two volumes resemble each other in
general structure. Both begin with a statement of what may be called the
mechanism of evolution,--variation and selection: in both the argument
proceeds from the