Will be proud to receive EH’s Die Radiolarien [1862].

Health continues very weak.

[P.S. 3 Jan] Has sent EH another letter by mistake.

Has received EH’s Die Radiolarien. Drawings admirably executed. Had no idea such low animals could develop such beautiful structures.

Thanks for paper ["Über die Entwicklungstheorie Darwins", Amtl. Ber. Versamml. Dtsch. Naturforsch. Aerzte 38 (1863): 17–30]. Delighted EH confirms his views. Many in England afraid to express views openly.

Thanks for praise [of Origin].

Comments on EH’s Die Radiolarien.

Grieved EH has suffered calamity [death of Anna Sethe Haeckel].

CD recovering from long illness.

Doing easy botanical work.

Mentions variability.

Discusses reception of CD’s views in Germany.

Can understand EH’s feelings on death of his wife.

CD was impressed by manner in which species in South America are replaced by closely allied ones, by affinity of species inhabiting islands near S. America, and by relation of living Edentata and Rodentia to extinct species. When he read Malthus On population, the idea of natural selection flashed on him.

Agrees with EH’s remarks on Kölliker ["Darwin’sche Schöpfungstheorie", Z. Wiss. Zool. 14 (1864): 174–86].

Asks EH to thank Carl Gegenbaur [for Vergleichende Anatomie der Wirbelthiere (1864)].

Sends Living Cirripedia [vol. 2].

Has employed translator for Fritz Müller’s book [Für Darwin (1864)].

Thanks for paper and speech.

Not surprised at delay of his book [Generelle Morphologie (1866)].

P. M. Duncan taking side of evolution.

Has received paper on Geryonidae ["Über eine neue Form des Generationswechsels bei den Medusen", Monatsber. K. Akad. Wiss. Berlin (1865): 85–94]. Had often speculated on whether such a case ever occurred in nature.

Sends copies of photographs of himself. Asks for photographs of German naturalists.

Comments on EH’s account of Protogenes primordialis.

Thanks for photographs [of German scientists].

Comments on sheet of EH’s Generelle Morphologie [1866]. In emphasising divergence of character EH shows his clear understanding of CD’s views. It was years before CD saw necessity of divergence.

Interested in Carl Claus [Copepodenfauna von Nizza (1866)].

Explains how to get to Down for visit.

Comments on EH’s "great work" [Generelle Morphologie].

An English translation "hopeless".

Asks about EH’s expedition.

MS of Variation sent to printers.

Fritz Müller working on plants.

Struck by singular clarity of EH’s Generelle Morphologie. Remarks on various authors seem too severe. Severity leads the reader to take the side of the attacked person.

Making slow progress in correcting Variation.

Discusses his previous criticisms of EH’s Generelle Morphologie. Fears it will make enemies.

Discusses reception of descent theory in England.

Mentions EH’s trip to Canary Islands.

Congratulates EH on approaching marriage.

Sorry he will not visit in autumn.

Glad EH is re-examining Protoamoeba but puzzled to think what he can find.

Describes newspaper account of criticism by Agassiz of Generelle Morphologie.

Delighted to hear of success of EH’s lectures.

Ernest Faivre [La variabilité des espèces (1868)] sees no reason to favour common descent of allied species.

Asks EH to pass German edition of Variation on to Gegenbaur.

Comments on work of Miklucho[-Maclay], Dohrn, and Bleek.

Has begun work on Descent.

Now understands importance of swim-bladder in selachians. Always imagined animal like Lepidosiren was parent form of vertebrates.

Has been nearly a month in London, collecting facts on sexual selection from breeders and at Zoological Gardens.

Astonished at hybrid of rabbit and hare. Is it certain that work was done with hare?

Thanks for two small works.

Will read essay on man [Entstehung des Menschengeschlechts] with much interest.

Generelle Morphologie reviewed by G. Bentham ["Anniversary Address", Proc. Linn. Soc. Lond. (1867–8): lviii–c].

Extremely sceptical of hare–rabbit hybrid.

Thanks for [Natürliche] Schöpfungsgeschichte [1868]. "What an indomitable worker you are."

Agrees with EH’s Entstehung des Menschengeschlechts [1868].

Congratulates EH on birth of child.

Mentions projected translation of Generelle Morphologie.

Comments on EH’s last book [Natürliche Schöpfungsgeschichte]. Criticises EH’s statements on palaeontology.