There are, however, certain facts familiar to the cytologist that furnish a clue as to how such an interchange might take place.
"Sex-linked Inheritance in Drosophila"
Thomas Hunt Morgan Calvin B. Bridges
Another deeply interesting letter of Darwin's bearing upon protective resemblance, has only recently been shown to me by my friend Professor E.B. Wilson, the great American cytologist.
"Darwin and Modern Science"
A.C. Seward and Others