424 SYNOPTIC COLLECTION. 



The prothorax is of good size and aids the head and 

 mouth organs, but the mesothorax is reduced in size and 

 bears the tiny scales which will probably in time wholly 

 disappear, while the metathorax is already a vestige with- 

 out appendages. 



Most specialized of all the Heteroptera are the parasi- 

 tic lice. Here the thoracic segments are fused together 

 and even the sutures are indistinct (PL 1055, the body 

 louse, Pediculus vestimenti Nitzsch ; hair line indicates 

 natural size) or apparently wanting (PI. 1056, the swine 

 louse, Haematopinus suis Leach) until brought out by 

 staining reagents. When thus brought into view, they 

 are proofs of the evolutionary history through which these 

 parasites have passed and demonstrate that the position 

 of these insects in a natural classification must be with 

 the secondary and specialized forms. Associated with 

 this specialization of the thorax is the loss of compound 

 eyes and the absence of both pairs of wings. The suck- 

 ing tube has lost its joints, is fleshy and capable of exten- 

 sion by rolling inside out. The feet have ceased to be 

 running or leaping organs, but are provided with claws 

 for climbing upon hairs or for clinging to the flesh of the 

 host. 



The generalized Homoptera are represented by the 

 Cicadidae. The seventeen-year species, Tibicen septende- 

 fim Linn., often called cicada (PI. 1057, larva; No. 

 1058, adult), requires that period of time for its develop- 

 ment in the north, and thirteen years in the south ; Cicada 

 marginata Say, (No. 1059, pupa skin; No. 1060, ^ ; No. 

 1 06 1, 9 ) probably develops in a shorter time, while our 

 common dog-day cicada, C. canicularis Harr. (PL 1062, 

 probably larva ; No. 1063, pupa skin and adult) reaches 

 the adult stage in two years (Comstock). There is little 

 in the larva of this insect that suggests the Thysanuran 

 stock form, although in certain characters the larva of the 

 seventeen-year cicada when newly hatched (PL 1057, 

 fig. i) approaches the Thysanura nearer than the proba- 



