1917] Morphology of Genitalia of Insects 125 



c. Hemiptera. — In many species of this order we meet the 

 problem presented by Berlese's theory of successive pairs of 

 cerci, which he illustrated by many examples from the Hemip- 

 tera. At the posterior end of Benacus, Zaitha and other species 

 of aquatic Hemiptera, in both the male and female there pro- 

 jects a pair of strap-like appendages, included by some authors 

 among the genitalia. Upon a close examination they are found 

 to be outgrowths of the eighth tergites, and the corresponding 

 pair of spiracles is situated at their bases. From these spiracles 

 two parallel rows of closely set setae extend to the distal ends of 

 these projecting tergites. Various observers have believed 

 them to be organs used in connection with the respiration of 

 these aquatic species. The seventh tergite of Benacus presents 

 a similar modification, and it contains the seventh pair of spir- 

 acles, but it is much broader and shorter. The seventh and 

 eighth tergites of Notonecta and the eighth tergite of Corixa 

 are apparently lengthened in like manner, and, according to 

 some investigators, have also a Hke function. Euschistus 

 variolarius and Anasa tristis, among the land forms, show similar, 

 projections from the tergites of this region, but lack the arrange- 

 ments of setas which have to do with the respiration of the 

 aquatic species. However, in neither case are these parts sep- 

 arated from the sclerite proper, as is always true of the cerci, 

 whether or not they show segmentation. In this connection, 

 it may be noted that these prolongations in the Hemiptera, 

 called by Berlese the cerci, are never segmented. The Hemip- 

 tera form a generalized order of insects, yet they are among the 

 most specialized of those having an incomplete metamorphosis. 

 There are, therefore, few appendages present in certain of 

 the more highly developed species, as is evident from the fol- 

 lowing table, and they are also specialized by modification in the 

 form of complicated mechanisims. Examples of the latter are 

 seen in the males of both Euschistus and Anasa. 



