The male genitalia, particularly the claspers and certain details of the vesica, have been used previously to define species of Miridae, and to a certain extent to determine their relationships. Reuter (1883), and particular Knight (1917), showed the differentiating characters in the claspers, and Knight (1923), Wagner (1940), Southwood (1953), and Kelton (1955) demonstrated that the details of the vesica might be used in specific determinations and as indicators of relationship.
However, the basic structural pattern of the vesica has not previously been tested or observed for stability within large groups, or its significance in the classification of the Miridae determined. This is a report on a comparison of the male copulatory structures and their modifications within the tribes and subfamilies, and on the phylogenetic relationships between species, genera, and higher categories of the family. The study indicates where the present classification, based on external characters, is somewhat unsatisfactory, and where more intensive work is needed to throw some light upon generic relationships.