text: Remarks: Common true katydids vary geographically not only in song but also in structure of the male cerci and subgenital plate. Treating all variants as populations of a single species accords with the observation that individuals of intermediate characteristics occur where populations of contrasting types come in contact. Such individuals are evidence of matings and gene flow between populations. The best studied contact zone is between northern and southeastern song types along the Appalachian Mountains. R. D. Alexander and K. C. Shaw drove back and forth across the zone at night listening to hundreds of thousands of individuals and tape recording hundreds ( Alexander 1968 ). Sometimes the two song types were kept apart by natural or manmade ecological barriers, but when they came in contact there was generally a zone of intermediates varying in width "from a few yards to more than a hundred miles."
  References: Balsbaugh 1988 ; North & Shaw 1979 ; Shaw 1968 , 1975 ; Shaw & Carlson 1969 ; Weissmann & Leatherman 1992 .
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