Charles Darwin an Ernst Haeckel, Down, 19. Juli 
Down Bromley Kent | July 19
I have been deeply interested by your most kind letter. – I naturally feel much curiosity on the progress of opinion on the descent of species, & I am delighted to hear that the subject is progressing in Germany which so abounds with great naturalists. – But what you tell me about yourself interests me the most, & I thank you sincerely for your confidence. I feel what you say in praise of my book & your intention of carrying onwards & perfecting the subject, as by far the greatest honour which could be paid me. I was shewn in London your magnificent work || on Radiolariæ. The passage which you refer to was pointed out to me & I was struck by it & admired the boldness of your expressions.
I am grieved to hear that you have suffered any heavy calamity; but at so early a period of life I cannot but hope that time, the great allayer of all evils, will do much for you. I am rendered by ill-health old for my years, which are 56, but I still feel a lively interest on many subjects, & your letter has delighted me. I have thought that perhaps you would like to have a photograph of me (lately taken by one of my sons) & which I enclose. Some time I hope that you will have the goodness to send me your photograph, as I should much like to possess a copy. || I am very much obliged for your promised book, which I will read with care, for what you say on individual variability in the Coelenterata is very remarkable; & this kind of variability has been greatly neglected by naturalists. I have however a very bad head for languages; & every German book takes me a long time which is a great evil, there is so much to read in German. I am slowly recovering from a long illness, which has quite prevented all work; but I hope soon to resume my nearly finished book on “Variation under Domestication”; in the mean time, I have been doing a little easy Botanical work, & one of the papers which I have prepared, will possibly interest you as it relates to reproduction & when printed I will send you a copy.
This kind of work being in some degree || new to me, I have been much struck with the interest which the theory of descent & modification gives to all researches in Natural History; for I was able to use my own views with a feeling of novelty almost as if I had only lately learnt them.
Pray present my respects to Schleicher & Gegenbaur. I am much pleased to know that men so distinguished agree to a large extent with my views.
Accept my cordial thanks for your long letter which has interested me in a high degree
I remain with much respect
yours very sincerely