that of
the temperate forms in the southern hemisphere, common to the north. I
remember writing about this after Wallace's book appeared, and hoping
that you would take it up. The frequency with which the drainage from
the land passes through mountain-chains seems to indicate some general
law--viz., the successive formation of cracks and lines of elevation
between the nearest ocean and the already upraised land; but that is too
big a subject for a note.

I doubt whether any insects can be shown with any probability to have
been flower feeders before the middle of the Secondary period. Several
of the asserted cases have broken down.

Your long letter has stirred many pleasant memories of long past days,
when we had many a discussion and many a good fight.

LETTER 399. TO J.D. HOOKER. Down, August 21st, 1881.

I cannot aid you much, or at all. I should think that no one could
have thought on the modification of species without thinking of
representative species. But I feel sure that no discussion of any
importance had been published on this subject before the "Origin,"
for if I had known of it I should assuredly have alluded to it in the
"Origin," as I wished to gain support from all quarters. I did not then
know of Von Buch's view (alluded to in my Historical Introduction in all
the later editions). Von Buch published his "Isles Canaries" in 1836,
and he here briefly argues that plants spread over a continent and
vary, and the varieties in time come to be species. He also argues that
closely allied species have been thus formed in the SEPARATE valleys of
the Canary Islands, but not on the upper and open parts. I could lend
you Von Buch's book, if you like. I have just consulted the passage.

I have not Baer's papers; but, as far as I remember, the subject is not
fully discussed by him.

I quite agree about Wallace's position on the ocean and continent
question.

To return to geographical distribution: As far as I know, no one ever
discussed the meaning of the relation between representative species
before I did, and, as I suppose, Wallace did in his paper before the
Linnean Society. Von Buch's is the nearest approach to such discussion
known to me.

LETTER 400. TO W.D. CRICK.

(400/1. The following letters are interesting not only for their own
sake, but because they tell the history of the last of Mr. Darwin's
publications--his letter to "Nature" on the "Dispersal of Freshwater
Bivalves," April 6th, 1882