42 THE UNIVERSITY SCIENCE BULLETIN. 



In the Typhlocybini their venation is of importance in the 

 separation of the genera, otherwise they are not much used 

 systematically. 



The abdomen consists of a number of distinct segments, 

 but the segmentation of the terminal portion is indistinct. 

 Each segment consists of two pieces, a dorsal tergum and a 

 ventral sternum. These are connected by 'pleural membranes. 

 There are eight distinct tergites, the last one being called the 

 pygofer. This sclerite is usually more or less divided caudo- 

 dorsally and through this excision rises the anal tube which 

 bears the anus at its apex. The question as to the number of 

 segments composing the anal tube is an interesting one and 

 one that requires careful study. In the female the pygofers 

 nearly enclose the ovipositor which is composed of three pairs 

 of valves. The pygofers are usually exceeded in length by the 

 ovipositor. 



The terminal sternites are of importance in classification. 

 In the female, in many genera, the last sternite is characteristic 

 of the species and is much used in differentiating them. In 

 a comparatively few species this Uist ventral segment is de- 

 scribed as being composed of an outer and inner membrane. 

 This is the case in the Deltocephalus compactus-weedi group. 

 It may be that a careful study with caustic potash specimens 

 will reveal the existence of such a condition in many more, if 

 not in all of the Cicadellidse. 



In the male the sternite just before the valve is called the 

 last ventral stetmite. The valve is usually a small and tri- 

 angular sclerite situated just before the plates. In many 

 genera the valve is described as lacking, but it seems more 

 probable that it is never absent, but only apparently so be- 

 cause it is often overlapped by the last ventral segment. It 

 is of great value in classification. In some genera, however, 

 it cannot be much used. 



Just caudad of the valve is a pair of usually triangular 

 sclerites, called plates. These also are often much used in 

 classification. They are fastened to the posterior margin of 

 the valve. Their homology brings up a question yet to be 

 worked out, for the question at once arises as to whether they 

 represent the divided sternite of the ninth abdominal seg- 

 ment, or whether they are paired reproductive appendages, 

 derived as are the other reproductive appendages from primi- 



