gions, for which they are by their nature
peculiarly adapted. Each species had only one beginning in a single
stock: probably a single pair, as Linnaeus supposed, was first called
into being in some particular spot, and the progeny left to disperse
themselves to as great a distance from the original centre of their
existence as the locomotive powers bestowed on them, or their capability
of bearing changes of climate and other physical agencies, may have
enabled them to wander." (14/9. Prichard, third edition, 1836-7, Volume
I., page 96.)

The second passage is annotated by Mr. Darwin with a shower of
exclamation marks:

"The meaning attached to the term SPECIES in natural history is
very definite and intelligible. It includes only the following
conditions--namely, separate origin and distinctness of race, evinced
by the constant transmission of some characteristic peculiarity of
organisation. A race of animals or of plants marked by any peculiar
character which has always been constant and undeviating constitutes a
species; and two races are considered as specifically different, if
they are distinguished from each other by some characteristic which one
cannot be supposed to have acquired, or the other to have lost through
any known operation of physical causes; for we are hence led to conclude
that the tribes thus distinguished have not descended from the same
original stock." (14/10. Prichard, ed. 1836-7, Volume I., page 106. This
passage is almost identical with that quoted from the second edition,
Volume I., page 90. The latter part, from "and two races...," occurs in
the second edition, though not quoted above.)

As was his custom, Mr. Darwin pinned at the end of the first volume
of the 1841-51 edition a piece of paper containing a list of the pages
where marked passages occur. This paper bears, written in pencil, "How
like my book all this will be!" The words appear to refer to Prichard's
discussion on the dispersal of animals and plants; they certainly do not
refer to the evolutionary views to be found in the book.)

LETTER 15. TO J.D. HOOKER. Down [1844].

Thank you exceedingly for your long letter, and I am in truth ashamed
of the time and trouble you have taken for me; but I must some day write
again to you on the subject of your letter. I will only now observe that
you have extended my remark on the range of species of shells into the
range of genera or groups. Analogy from shells would only go so far,