HEMIPTERA. 



!59 



/ 2- 



Fig. 133. — Wings of Plant-louse. 



133, sc,) is the subcostal or submarginal vein. The distal end of 

 this vein becomes widened, and ex- 

 tends to the margin of the wing; this 

 part of it is the stigma (st). From the 

 stigma, a curved vein extends to the 

 tip of the wing; this is the stigmatic 

 or fourth vein. From the submarginal 

 vein there branch two or three veins 

 (in addition to the stigmatic vein), 

 which extend across the disk of the 

 wing ; these are the first, second, and 

 third discoidal veins. The third dis- 



coidal vein is sometimes forked. The veins of the hind wing, so 

 far as they are present, are named in a similar manner. 



A. Winged form known; species not subterranean, except in a few cases 

 where there are dimorphic forms. 



B. Front wings with three discoidal veins ; antennae of the winged individu- 

 als, and generally of the apterous individuals, six- or seven-jointed. 

 C. Front wings with the third discoidal vein twice forked (except in Tox- 

 optera, which, however, has well-developed honey-tubes); posterior 

 wings with two discoidal veins ; honey-tubes various. 4. AphidiX/E. 



CC. Third discoidal vein with one fork or simple ; posterior wings with 

 one or two oblique veins; honey-tubes tuberculiform or want- 

 ing. 3. Pemphigix.'e. 

 B. Front wings with but two discoidal veins, the third being absent ; an- 

 tennae never more than five-jointed, sometimes but three-jointed. 



2. CHERMESIN/E. 



A A. Permanently apterous ; at least no winged form has been observed : chiefly 

 subterranean, residing on the roots of plants. 1. Rhizobiix.e. 



Sub-Family I. — RinzOBIIN/E.* 



As indicated in the table above, this sub-family has been erected 

 for certain genera in which no winged forms are known. It is pos- 

 sible that some of the insects placed here are merely the degraded 

 wingless generation of species which have also higher developed 

 forms with wings, and which pertain to some one of the three higher 

 sub-families. 



The Rhizobiina live in the ground upon the roots of plants. 

 Our best known representative is the Lettuce Earth-louse, Rhizobius 

 lactucce. This occurs on the roots of lettuce, often in great Hum- 



* Rhizobilnse, Rhizobius; rhiza (pi%a), root; bios (fSiof), life. 



