METCALF: HOMOPTERA AUCHENORHYNCHA 529 



date; da Fonseca, 1926 to date; Kato, 1925 to date; Kiisnetzov, 1925-1938; Lind- 

 berg, 1923 to date; Muir, 190G-1934; Nast, 1933 to date; Oman, 1930 to date; 

 Ossiannilsson, 1934 to date. 



I have listed above the men who have been cliiefly responsible for our present- 

 day concepts of the systematics of the group. Many other students of mor- 

 phology, phylogeny, fossil insects, physiology, ecology, and especially economic 

 entomology have contributed greatly to our knowledge, but their numbers are 

 so large that it is not possible to evaluate here their contributions. 



Our next purpose is to summarize very briefly the developments that have 

 taken place in the study of the Homoptera. Before 1853 most students of ento- 

 mology devoted themselves almost exclusively to the larger and more conspicuous 

 insects; and the Homoptera, particularly the smaller leaf hoppers, planthoppers, 

 and froghoppers, were largely neglected. The larger and more conspicuous sing- 

 ing cicadas and a few of the more conspicuous treehoppers, particularly those 

 from South America, received some attention. 



More and more attention, however, has been devoted not only to the smaller 

 Homoptera of Europe and North America in particular but from various parts 

 of the world. It was in this period also that Fieber, studying the smaller Euro- 

 pean planthoppers of the family Araeopidae, emphasized the importance of a 

 careful study of the details of the male genitalia. Fortunately, in this family 

 there are abundant characters in the external male genitalia for determining 

 most species, and it is not necessary to make elaborate dissections and clear 

 these parts in order to appreciate the importance of these characters. 



Unfortunately, however, Fieber's contribution was almost completely neg- 

 lected for fifty years, while students devoted themselves to the finer and finer 

 details of the external anatomy of the insects of this order and did not study the 

 internal genitalia. Increasing attention was given, for example, to the relative 

 proportion of parts, particularly the length and breadth of the face, of the 

 crown, of the pronotum, of the mesonotum; some attention was paid to wing 

 venation and some to the external characters of the male and female genitalia, 

 particularly the last ventral jjlate of the female in the leafhoppers and the 

 proportions of the valve in the male. But beginning about 1920 students of Ho- 

 moptera placed increasing emphasis on the details of the various structures 

 revealed by careful dissection and clearing of the male genitalia. In this connec- 

 tion one may point out that perhaps too much emphasis has been placed upon 

 the fine details of the aedeagus. Subsequent studies may show, however, that 

 even greater emphasis is needed on the study of this structure and that what 

 we now consider good genital characters for the differentiation of species are 

 of generic, not specific, value. On the other hand, perhaps too little emphasis 

 has been placed upon the general picture of the male and female genitalia as 

 generic characters. And I believe that one of the developments for the future 

 will be in this particular area. 



In other areas, however, the study of the Homoptera has not kept pace with 

 the development of taxonomie studies. Fairly comprehensive studies have been 

 made in the general morphology of the head, of the wings, and of the male geni- 

 talia. Still more detailed work needs to be done in all of these areas and par- 

 ticularly in the morphology of the thoracic sclerites before we have a compre- 

 hensive view of the morphology of this interesting group of insects. 



