Offers enclosure demonstrating that natural selection could produce sterility of hybrids.
More on Pangenesis and the inadequacy of H. Spencer’s approach.
On critical exchanges at the Linnean Society on natural selection and mimicry.
Roland Trimen’s paper on South African mimetic butterflies ["On some remarkable mimetic resemblances among African butterflies", Trans. Linn. Soc. Lond. 26 (1870): 497–523; read 5 Mar 1868].
Coloration of butterflies; brilliantly coloured females.
Commends CD on his paper on specific differences in Primula [J. Proc. Linn. Soc. Lond. (Bot.) 10 (1869): 437–54; reprinted and revised in Forms of flowers] as a test-case proving origin of real species.
On his Primula paper for the Linnean Society ["On the specific difference between Primula veris, Brit. Fl. (var. officialis, Linn.), P. vulgaris, Brit. Fl. var. acaulis, Linn.), and P. elatior, Jacq.; and on the hybrid nature of the common oxlip; with supplementary remarks on naturally produced hybrids of the genus Verbascum", [officinalis!?] J. Linn. Soc. Lond. (Bot.) 10 (1869): 437–54].
Peacocks and sexual selection.
ARW’s sterility argument has driven CD’s sons half-mad.
On sterility of natural species and natural selection. Closely allied forms from adjacent islands offer best chance of finding good species fertile inter se.
Problem of minute variations and sexual selection.
On problem of sterility, CD cannot persuade himself that it has been gained by natural selection.
On sexual selection and minute variations, he tends to agree with ARW. Sends George Darwin’s notes on ARW’s argument.
Returns George Darwin’s criticisms of his notes on sterility and sends further notes in reply. Since there are degrees of sterility between varieties, "is it not probable that natural selection can accumulate these variations?" Varieties that are adapted to new conditions could then survive and form new species without being isolated.
There are so many doubtful points on the problems relating to sterility that they will never agree.