| Letter from Charles Darwin to J.-H. Fabre of January 31, 1880 | 151 |
| Letter from Charles Darwin to J.-H. Fabre of February 20, 1880 | 94 |
| Letter from Charles Darwin to J.-H. Fabre of January 21st, 1881 | 100 |
| Letter of Charles Darwin to G.J. Romanes of April 16, 1881 | 96 |
