Rizki MT

Proc Natl Acad Sci U S A. 1951 Mar;37(3):156-9. doi:10.1073/pnas.37.3.156

Morphological differences between two sibling species; Drosophila pseudoobscura and Drosophila persimilis.

The first morphological difference that distinguishes D. persimilis from D. pseudoobscura: penis size.