(A) Phylogenetic tree showing the relationship between four Drosophila species. The posterior lobe is a projection (indicated by a teal arrow) from the lateral plate that first appeared in the common ancestor of D. sechellia and D. melanogaster. The lobe is not found in D. biarmipes or D. ananassae; asterisk indicates the position on the lateral plate corresponding to the position of the lobe in the other two species. (B) In D. sechellia and D. melanogaster the extracellular matrix (pink) covers the entire apical side (the outer side) of the genitalia, including the elongating posterior lobe (PL) and clasper (C). In D. biarmipes or D. ananassae the matrix does not reach the region corresponding to the lateral plate (LP: asterisk).