Permit me to add that I have never been so foolish as to imagine that I have succeeded in doing more than to lay down some of the broad outlines of the origin of species.
After long reflection I cannot avoid the conviction that no innate tendency to progressive development exists, as is now held by so many able naturalists, and perhaps by yourself.

It is curious how seldom writers define what they mean by progressive development; but this is a point which I have briefly discussed in the "Origin." I earnestly hope that you may visit Hilgendorf's famous deposit.

Have you seen Weismann's pamphlet "Einfluss der Isolirung," Leipzig, 1872?
He makes splendid use of Hilgendorf's admirable observations.

(254/2.

Hilgendorf, "Monatsb.
K.Akad." Berlin, 1866.