INSECTS. m 



its prey; the Argyronetra aquatica lives in air-bubbles under water; 

 and the Attus volans of Australia has flaps or wing-like extensions of 

 the abdomen, that it elevates or depresses during leaps from plant to 

 plant. The egg-sacs (Fig. 132, a) are sometimes attached to the webs, 

 carried about by the mother, or affixed to stalks (Fig. 132, b\ and re- 

 semble small plants. 



VALUE. Spiders are useful in destroying other noxious insects. 

 The silk is of value to opticians as cross-lines in optical instruments, 

 also as a mechanical styptic. The silk of certain spiders has been 

 woven. One of the kings of France possessed a coat made of this silk. 

 In Bermuda the silk of Nephila has been used as sewing-silk. 



Works on Spiders for further reference. 



" Structure and Habits of Spiders," J. H. Emcrton.; "Harvesting 

 Ants and Trap-door Spiders," J. T. Moggriclge ; "The Triangle Spi- 

 der," B. G. Wilder, " Popular Science Monthly," 1875 ; " Practical 

 Use of Spider-Silk," B. G. Wilder, the "Galaxy," July, 1869 ; " Pedi- 

 palpi of North America," H. C. Wood, Jr., "Journal of Philadelphia 

 Academy of Natural Science," vol. v ; " Mites, Ticks, and other Aca- 

 ri," ' Popular Science Monthly," vol. xiv ; " Termayer's Researches 

 on Spiders' Silk," "Proceedings of Essex Institute," vol. v; " Pha- 

 langerae of the United States," H. C. Wood, Jr., " Proceedings of Essex 

 Institute," vol. vi ; " Harper's Monthly," vol. Ix, Treat. Packard's 

 " Guide to the Study of Insects." 



Sub-Class IV. SIX-LEGGED INSECTS (ffexapoda). 

 i 



General Characteristics. The Hexapods have antennae 

 and two pairs of jaws or maxillae. 



FlG. 133. Glacier-flea (Desoria glacialis). 



Order I. Spring-Tails (Thysanura). The spring- 

 tails are minute wingless forms that possess a forked spring. 



