London, Nature, 1876. Folio (28.2 x 19.6 cm). pp. 17-18 in: Nature issue 15(366) [pp. i-viii, 1-20]. Original printed wrappers.

This paper by Darwin deals with the "brightly coloured hinder ends ... of certain monkeys", of which Darwin wrote: "no case interested and perplexed me so much". Darwin continued by recording and interpreting observations made by the German zoologist Johann von Fischer (1850-1901), to whom he wrote a long letter. As noted by Freeman (p. 204), this paper was reprinted in The Descent of Man, 12th thousand, 1877 (Freeman, 948), and later printings. Uncut, as issued. Small strip of front wrapper's left outer edge evenly tanned; otherwise a very good, clean copy. Burkhardt, F. et al. (eds.), The Correspondence of Charles Darwin, volume 24; Freeman, 1773.