Down, November 20th, 1869.
Dear Sir, I am glad that you are a candidate for the Chair of Physiology in Paris.
As you are aware from my published works, I have always considered your investigations on the production of monstrosities as full of interest.
No subject is at the present time more important, as far as my judgment goes, than the ascertaining by experiment how far structure can be modified by the direct action of changed conditions; and you have thrown much light on this subject.
I observe that several naturalists in various parts of Europe have lately maintained that it is now of the highest interest for science to endeavour to lessen, as far as possible, our profound ignorance on the cause of each individual variation; and, as Is.

Geoffroy St.Hilaire long ago remarked, monstrosities cannot be separated by any distinct line from slighter variations.
With my best wishes for your success in obtaining the Professorship, and with sincere respect.
I have the honour to remain, dear sir, Yours faithfully, CHARLES DARWIN..