282 THE WINGS OF JASSIDM 



The wings of the Jassidse show marked specialization by reduction. 

 This reduction is usually accompanied by the atrophy of one of the branches 

 of one of the main tracheae and the shifting of a branch of a neighboring 

 trachea until it occupies the region of the atrophied trachea. The atrophy 

 of these tracheae with the subsequent shifting of other trachea which take 

 their places gives to the wings of the Jassidse their characteristic aspect. 



The casta of the fore wing. — The costal trachea was absent in all of the 

 jassid wings examined with the exception of Gypona (Fig. 284, 8). This 

 indicates that the costal trachea has practically disappeared from the 

 Jassidae. 



The suhcosta of the fore wing. — A subcostal trachea was found in only 

 six of the genera examined; among these are Agallia (Fig. 284, i) and 

 Gypona (Fig. 284, 8). A subcostal vein, however, is well developed in all of 

 the adult wings studied, and it shows very clearly as a distinctly lighter 

 area in all of the older nymphs examined. 



The radius of the fore wing. — The radial trachea of the fore wing of 

 Jassidse is typically two-branched although in some forms three or even four 

 branches do occur. The two branches of the typical radius represent 

 R2+3 and R4+5. Ri has almost completely disappeared from the fore 

 wings in this family. It does occur, as a delicate branch in a few genera 

 (Fig. 284, 3) but gives rise to a very characteristic cross- vein between sub- 

 costa and radius, which is known currently as the "nodal vein." 



The media of the fore wing. — The medial trachea is typically two 

 branched in the Jassidae. These branches are Mi +2 and M3+4. Trachea 

 Mi+2 is well developed in only a few genera; in Gypona (Fig. 284, 8) it is 

 vestigial; in the other fore wings represented in this figure the medial 

 trachea is reduced to an unbranched condition ; and this is the case in most 

 of the forms examined by Metcalf . 



The cubitus and the first anal of the fore wings. — In all of the genera of 

 the Jassidae examined the cubital and the first anal tracheae were the most 

 constant and formed one of the best landmarks in the study of the relations 

 of the tracheae. They coalesce for some little distance from the base of 

 the wing. 



The cubital trachea is frequently two-branched (Fig. 284, 8) ; but in the 

 greater ntimber of genera studied by Metcalf it is reduced to an unbranched 

 condition. The presence of forms in which trachea Cu2 is reduced to a 

 mere spur indicates that it is this branch that is lost in those foniis where 

 the cubital trachea is unbranched. 



The first anal vein of the fore wings.- — The first anal vein lies along the 

 anal border of the claval suture. It has not been usually recognized as a 

 distinct vein owing to the fact that as a vein it is rather inconspicuous while 

 the claval suture or fold is very distinct. It is, however, preceded by a 

 conspicuous trachea in all of the genera studied. 



