I finished your book yesterday, a lucky examination having furnished me
with a few hours of continuous leisure.

Since I read Von Baer's (Karl Ernst von Baer, born 1792, died at Dorpat
1876--one of the most distinguished biologists of the century. He
practically founded the modern science of embryology.) essays, nine years
ago, no work on Natural History Science I have met with has made so great
an impression upon me, and I do most heartily thank you for the great store
of new views you have given me. Nothing, I think, can be better than the
tone of the book, it impresses those who know nothing about the subject.
As for your doctrine, I am prepared to go to the stake, if requisite, in
support of Chapter IX., and most parts of Chapters X., XI., XII., and
Chapter XIII. contains much that is most admirable, but on one or two
points I enter a caveat until I can see further into all sides of the
question.

As to the first four chapters, I agree thoroughly and fully with all the
principles laid down in them. I think you have demonstrated a true cause
for the production of species, and have thrown the onus probandi that
species did not arise in the way you suppose, on your adversaries.

But I feel that I have not yet by any means fully realized the bearings of
those most remarkable and original Chapters III., IV. and V., and I will
write no more about them just now.

The only objections that have occurred to me are, 1st that you have loaded
yourself with an unnecessary difficulty in adopting Natura non facit saltum
so unreservedly...And 2nd, it is not clear to me why, if continual physical
conditions are of so little moment as you suppose, variation should occur