CLASS INSECTS. 



453 



The history of this singular and most destructive insect cannot 

 fail to excite deep reflections in the mind of the reader, as show- 

 ing by what apparently insignificant means, entire races of 

 valuable animals may be destroyed. Many wild species of the 

 equine family and of the buffalo exist in Southern Africa, and 

 live with impunity, unscathed by the tsetse, the attacks of which 

 prove so fatal to certain domestic animals. The ass, though 

 domestic in a senee, is not injured by the tsetse ; so also with the 

 buffalo, and seemingly. all the species of antelope. Sheep also 

 are safe from its attacks. K. K.] 



Fig. 490. Stylops. 



Fig. 491. Pediculus humanus, 

 or Louse. 



Fig. 492. Machilis. 



548. Finally, the insects of the order thysanura com- 

 mence equally with the form which they preserve through 

 life, and are always without wings ; but they are distinguished 

 from the preceding by their masticatory apparatus, and by 



