HOMOPTERA 



395 



Figure 459 represents the tracheation of the fore wing of a 

 young nymph of a cicada. The dotted Hne a-h indicates approximate- 

 ly the line along which 

 the hinge of the wing 

 of the adult is formed. 

 In this wing the only 

 departures from the 

 typical branching of 

 the tracheee are the 

 following: trachea Ri 

 coalesces with the ra- 

 dial sector to a point 

 beyond the separation 

 of trachea R 1+5 from 

 the sector; the first 

 anal trachea coalesces 

 with trachea Cu for a 

 short distance; and 

 the second and third 

 anal tracheae are unit- 

 ed at the base. These 

 differences are remark- 

 ably slight compared with the great changes that have taken place 

 in the specialization of the mouth -parts and other organs of the 

 adult cicada. 



Figure 460 represents the fore wing of a mature nymph of a cicada. 

 In this wing trachea Ri is completely aborted. In fact one of the 



Fig. 459. — Tracheation of a fore wing of a young 

 nymph of a cicada. 



Fig. 460. — Tracheation of a fore wing of a mature nymph of a cicada. 



most characteristic features in the venation of the Homoptera, 

 and of the Hemiptera also, is the absence or very great reduction 

 of vein Ri in the adult wings of most members of these two orders. 

 In the stage represented in this figure the developing cross-veins 

 appear as pale bands. 



