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June 6 61/ The case of Primula just opposite to species; similar forms are here fully fertile dissimilar sterile; with Primula the similar are sterile & the dissimilar fertile.

Keep in Hybrid Chapt

As was seen sterility acquired merely to prevent intermarriage, & this can hardly be disputed by those who consider all above facts & who believe in change of species; so may we not ask whether sterility may not have been acquired to prevent blending of two incipiently divergent forms. As one became adapted for aquatic life would it not have been an advantage that it shd not have become blended with the truly terrestrial form— The first change may have been infinitely slight, the degree which

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My facts on Primula perhaps explain Gærtners ill-success in crossing Primrose & Cowslip. — Did not Lecoq succeed. I have succeeded with greatest ease.—

If we take broad view of good of Divergence— good of sterility follows —

In neuter insects sterility from loss of sexual instinct