In
far the greater number of points I quite follow you in your conclusions,
but I differ on some, and I suppose that no two men in the world would
fully agree on so many different subjects. I have been interested on
so many points, I can hardly say on which most. Perhaps as much on
Geographical Distribution as on any other, especially in relation to M.
Wagner. (No! no! about parasites interested me even more.) How strange
that Wagner should have thought that I meant by struggle for existence,
struggle for food. It is curious that he should not have thought of the
endless adaptations for the dispersal of seeds and the fertilisation of
flowers.

Again I was much interested about Branchipus and Artemia. (303/2. The
reference is to Schmankewitsch's experiments, page 158: he kept Artemia
salina in salt-water, gradually diluted with fresh-water until it became
practically free from salt; the crustaceans gradually changed in the
course of generations, until they acquired the characters of the genus
Branchipus.) When I read imperfectly some years ago the original paper
I could not avoid thinking that some special explanation would hereafter
be found for so curious a case. I speculated whether a species very
liable to repeated and great changes of conditions, might not acquire
a fluctuating condition ready to be adapted to either conditions. With
respect to Arctic animals being white (page 116 of your book) it might
perhaps be worth your looking at what I say from Pallas' and my own
observations in the "Descent of Man" (later editions) Chapter VIII.,
page 229, and Chapter XVIII., page 542.

I quite agree with what I gather to be your judgment, viz., that the
direct action of the conditions of life on organisms, or the cause of
their variability, is the most important of all subjects for the
future. For some few years I have been thinking of commencing a set of
experiments on plants, for they almost invariably vary when cultivated.
I fancy that I see my way with the aid of continued self-fertilisation.
But I am too old, and have not strength enough. Nevertheless the hope
occasionally revives.

Finally let me thank you for the very kind manner in which you often
refer to my works, and for the even still kinder manner in which you
disagree with me.

With cordial thanks for the pleasure and instruction which I have
derived from your book, etc.

LETTER 304. TO COUNT SAPORTA. Down, February 13th, 1881.

I received a week or