STOUGH : THE HACKBERRY PSYLLA. 145 



In the males there is generally a large dark spot between 

 Cu 1 and Cu 2, and on and below the radius proximad of 

 its fusion with the subcosta, this spot tending to spread 

 across cell I. These spots, proximad from the stigma, tend in 

 the female to be reduced to dusky portions only a little darker 

 than the surrounding parts, the former being almost indistin- 

 guishable and the latter confined to a border to the vein. The 

 three marginal spots mentioned by Riley are generally more 

 distinct in the male. There is a great deal of individual varia- 

 tion in the wing markings as to the number and arrangement 

 of the small spots composing the pattern, no two individuals 

 showing precisely the same combinations. Figures 1 and 5, 

 plate XXXIII, show how this pattern is produced, and inci- 

 dentally the difference in shape of the apices of the male and 

 female wings. Figure 4, plate XXXIII, is another view of the 

 pattern at the branching of the median veins, more highly 

 magnified than the two preceding. 



The upper surface of the wing is entirely covered with disk- 

 like cuticular outgrowths about 0.005 mm. in diameter, best 

 seen in cross section through the wing (30-9, a and b). These 

 are more or less circular in outline though often very irregular. 

 Some of these, b, are filled with dark brown pigment, the same 

 diffusing slightly into the surrounding cuticula. These pig- 

 mented disks are arranged in groups of 2, 3, 4, 5, 6, 7, 8, and 

 so on, to form polygons and other figures. These groups form 

 the "spots" which make up the pattern, and are either distinct 

 or banked up together to form a dark spot or band, in which 

 case the polygonal structure is not so apparent. The following 

 elements make up the pattern: (1) The individual pigmented 

 cuticular processes, which I shall designate as "disks"; (2) 

 polygonal and other combinations of these disks — "groups"; 

 (3) arrangements of these groups making up the large and 

 small spots, bands, etc. — "markings." 



There are a great many different forms of groups produced 

 by these disks, the principal types of which are seen on page 

 146. Polygonal groups predominate, though chainlike, broken, 

 and irregular forms are also found. Groups of "two's" and 

 "three's" arranged lengthwise with the wing are found pre- 

 dominating in the basal cells, while more complex polygonal 

 figures are the rule in the distal regions of the wing. Groups 

 consisting of only one disk were not found. 



Any difference between the composition of the groups or the 



