THYSANURA. 



553 



Locustidce, at the base of the anterior wings. Both sexes of the 

 Acrididce also produce similar though feebler chirping sounds, by 

 rubbing the femora of the posterior legs against the edge of the wing- 

 covers. 



Insects are almost universally distributed, from the equator to the 

 extreme limits of vegetation ; certainly with a considerable diminu- 

 tion in the number of species, and in their size and beauty of colour. 

 Some forms are truly cosmopolitan, e.g., Vanessa cardui. Fossil 

 insects are found in 

 increasing numbers of 

 species, from the car- 

 boniferous formation to 

 the tertiary period. The 

 best preserved are those 

 enclosed in amber and 

 the impressions in the 

 lithographic slate. 



Order 1. THYSANURA* 

 (including COLLEM- 

 BOLA). 



Wingless insects, with 

 hairy or scaly body cover- 

 ing ; with rudimentary 

 masticating mouth parts 

 and setiform anal fila- 

 ments, which may serve 

 as a springing appara- 

 tus, at the end of the 

 ten-segmented abdomen. 

 Development without 

 metamorphosis. 



The Thysanura seem to have preserved most completely the 

 primitive character of the oldest insect forms. The elongated 

 Campodidce particularly recall certain Myriapods, especially since 

 they may have rudimentary feet on the abdomen (fig. 459, a, b). 

 On this account the Campodidce have been regarded as ancestral 



FIG. 459. a, Campodea stapTtyUnnt (after J. LobbOCk). 



b, Anterior half of the body of C. fragilU (after 

 PalmtSn). Tr, Trachea; S, stigmata; P, legs; P' t rudi- 

 mentary abdominal feet; A, antenna?. 



* John Lubbock, '' Monograph of the 'Collembola and -Thysanura." Londor, 

 1873. 



