8 University of Michigan 



difficult. But in plant tissues, if it is in such situations that the 

 eggs are placed, such a structure would serve to steady or 

 maintain the ovipositor after it had been inserted. Likewise 

 the grooves of the posterior processes cannot, I think, aid 

 much in the insertion of the ovipositor. They lie generally 

 within the lateral edges of the anterior processes and between 

 these processes and the abdomen. Their function is probably 

 concerned with the extrusion of the ^gg. Venation : several 

 characters have been employed in describing groups or species. 

 The distance between the arculus and the cubito-anal cross- 

 vein, for example, can be measured with accuracy, for these 

 parts lie at approximately right angles to the longitudinal veins 

 bounding them. But the distance between the cubito-anal 

 cross-vein and the point of departure of the anal vein from 

 the posterior wing margin is an entirely different matter, as 

 the anal vein and the posterior wing margin meet in a very 

 acute angle. If the parts are viewed at such an angle as to 

 superimpose the anal vein on the wing margin near their 

 juncture point, the point of separation appears much more 

 distal than is really the case. In studying this character I have 

 held the plane of the wings at right angles to the line of vision, 

 and with the long axis of the wings at right angles to the ob- 

 server, studying them under a binocular microscope. With 

 these simple precautions one can detect the real point of separ- 

 ation with a fair degree of accuracy. There is a great differ- 

 ence in the width of the wings between species and, in some 

 cases, between the sexes of the same species. Wing narrow- 

 ness in this genus is brought about solely by the narrowing of 

 cells and no other change in the position of the larger veins 

 takes place. Hence the character can only be used with dif- 

 ficulty, especially since all gradations between the extremes 

 exist. The only way of expressing the character seems to be 



