The "kleine Schrift" is "Ueber die Berechtigung der Darwin'schen Theorie," Leipzig, 1868.

The "Anhang" is "Ueber den Einfluss der Wanderung und raumlichen Isolirung auf die Artbilding.") to which you allude; but I fear it is lost, which I am much surprised at, as I have seldom failed to receive anything sent by the post.
As I do not know the title, and cannot order a copy, I should be very much obliged if you can spare another.
I am delighted that you, with whose name I am familiar, should approve of my work.

I entirely agree with what you say about each species varying according to its own peculiar laws; but at the same time it must, I think, be admitted that the variations of most species have in the lapse of ages been extremely diversified, for I do not see how it can be otherwise explained that so many forms have acquired analogous structures for the same general object, independently of descent.

I am very glad to hear that you have been arguing against Nageli's law of perfectibility, which seems to me superfluous.

Others hold similar views, but none of them define what this "perfection" is which cannot be gradually attained through Natural Selection.