Notes the differences in haemoglobin between species; this proves, to WP, that natural selection does not act only on morphological development.

Remarks on the differences and similarities in the effects of prussic acid on different groups of animals.

Questions CD on his early education and influences.

Comments on effects of prussic acid on different individuals of the same species and other physiological research by WP.

Provides information about his studies in Edinburgh and Cambridge and qualifications he had for Beagle voyage. Describes influence of R. E. Grant and J. S. Henslow.

Sends his "Charles Darwin, eine biographische Skizze" [Das Ausland 2 Apr 1870].

Comments on WP’s biographical article on CD. Asks him to thank O. F. Peschel for his present of the publication [Das Ausland 2 Apr 1870].

Thanks CD for Origin, 5th ed.

Comments on reviews of Descent by the Duke of Argyll and A. R. Wallace.

Lists the Darwinian professors at Jena.

WP’s work shows external ear to have no physiological functions.

W. Müller’s book not yet arrived. Will send Müller’s next works.

Is sending copy of Descent.

Thanks for copy of WP’s book [Die Blutkrystalle (1871)].

Discusses shape of external ear.

Delighted that CD does not hesitate to follow his theory to its last consequences. "This is far more difficult in England than in Germany."

Wilhelm Müller in his new book [Beiträge zur pathologischen Anatomie und Physiologie des menschlichen Rückenmarks (1871)], adduces many facts in favour of CD’s theory.

Various observations on the human ear. [See Descent, 2d ed., p. 14 n.]

Obliged for letter about human ear. Comments on ears and on E. R. Lankester’s idea about the ear-lobe.

Asks for CD’s "Sketch of an infant" [Collected papers 2: 191–200]. He has made observations on new-born children and mammals to determine what behaviour is inherited and what acquired.

Discusses inheritance.

Has WP heard of Douglas Spalding’s experiments of blindfolding chickens ["Instinct – with original observations on young animals", Rep. BAAS 42 (1872): 141–3]?

Thanks WP for election [as honorary member of the Medicinisch-Naturwissenschaftliche Gessellschaft zu Jena].