study of domestic organisms to that of animals and
plants in a state of nature. This is followed in both by a discussion of
the _Difficulties on Theory_ and this by a section _Instinct_ which in
both cases is treated as a special case of difficulty.

If I had to divide the _Origin_ (first edition) into two parts without
any knowledge of earlier MS., I should, I think, make Part II begin with
Ch. VI, _Difficulties on Theory_. A possible reason why this part of the
argument is given in Part I of the Essay of 1842 may be found in the
Essay of 1844, where it is clear that the chapter on instinct is placed
in Part I because the author thought it of importance to show that
heredity and variation occur in mental attributes. The whole question is
perhaps an instance of the sort of difficulty which made the author give
up the division of his argument into two Parts when he wrote the
_Origin_. As matters stand Sec.Sec. IV. and V. of the 1842 Essay correspond to
the geological chapters, IX and X, in the _Origin_. From this point
onwards the material is grouped in the same order in both works:
geographical distribution; affinities and classification; unity of type
and morphology; abortive or rudimentary organs; recapitulation and
conclusion.

In enlarging the Essay of 1842 into that of 1844, the author retained
the sections of the sketch as chapters in the completer presentment. It
follows that what has been said of the relation of the earlier Essay to
the _Origin_ is generally true of the 1844 Essay. In the latter,
however, the geological discussion is, clearly instead of obscurely,
divided into two chapters, which correspond roughly with Chapters IX and
X of the _Origin_. But part of the contents of Chapter X (_Origin_)
occurs in Chapter VI (1844) on Geographical Distribution. The treatment
of distribution is particularly full and interesting in the 1844 Essay,
but the arrangement of the material, especially the introduction of Sec.
III. p. 183, leads to some repetition which is avoided in the _Origin_.
It should be noted that Hybridism, which has a separate chapter (VIII)
in the _Origin_, is treated in Chapter II of the Essay. Finally that
Chapter XIII (_Origin_) corresponds to Chapters VII, VIII and IX of the
work of 1844.

The fact that in 1842, seventeen years before the publication of the
_Origin_, my father should have been able to write out so full an
outline of his future work, is very remarkable. In his Autobiography{2