260 



APTEEA. 



of its own, either over a piece of water, along some lane, or 

 in some glade in a wood. There are some (LibelluUdce) which 

 are beautiful fragile insects (Calepteryx). The eggs are laid in 

 the water or on aquatic plants. The young (fig. 134, b) possess 

 no traces of wings. They commence to show after the third or 

 fourth moult (c, w). The nymph (c) has a much shorter body 

 than the adult, and, previous to hatching, crawls up the stem 

 of some water-plant, when the shell splits, and the perfect 

 Dragon-fly emerges. 



APTERA. 



Lastly, we have the wingless primitive insects, the Collem- 

 bvla and Tliijsaiiura, now united into one order, the Aptera. 

 They are popularly called " Spring-tails.'' 

 There are never any wings or rudiments 

 of such, hut always three pairs of legs, 

 and long or moderately long antemise. 

 They practically remain in the larval 

 stage thix)ughout life. The Thysanwa 

 have ten segments in the abdomen ; the 

 Collembola have six or less segments, 

 and the first one is always provided 

 ventrally with a curious tube, which is 

 absent in the Tliysanum. The Cd- 

 lembola have the power of leaping or 

 skipping intot he air : some have a long, 

 forked, ventral process towards the anus, 

 which is used as a leaping apparatus. 



Some Collembola are now and then 

 injurious {Smy7ithu}-iis), and a few Thy- 

 sanura are more or less noxious, as the Silver Fish (Lepisma 

 tiaccharina) (fig. 135), a curious silvery form found in 

 and in houses generally. 



Flu. 136.— Silver Fish 



{Lepisvia aaccharina). 



