APTEBA. 



289 



part of the head. They are provided with very powerful 

 mouths. Their wings are usually transparent, and have a 

 number of mesh-like veins. The legs have a series of spines 

 upon them. Dragon-flies are most useful as insect destroyers. 

 Each individual seems to have a hunting-ground of its own, 

 either over a piece of water, along some lane, or in some glade 

 in a wood. There are some (LihelluUdce) which are beautiful 

 fragile insects (Galepteryx). The eggs are laid in the water or 

 on aquatic plants. The young (fig. 167, b) possess no traces 

 of wings. They commence to show after the third or fourth 

 moult (c, w). The nymph (o) 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 CoUemhola 

 and TJiysanura, now united into one order, 

 the A]ptera. Many are popularly called 

 " Spring - tails." There are never any 

 wings or rudiments of such, but always 

 three pairs of legs, and long or moder- 

 ately long antennae. They practically 

 remain in the larval stage throughout life. 

 The Tliyscmura have ten segments in the 

 abdomen ; the CoUemhola have six or less 

 segments, and the first one is always 

 provided ventrally with a curious tube, 

 which is absent in the TJiysanura. The 

 Gollenihola have the power of leaping or 

 skipping into the air : some have a long, 

 forked, ventral process towards the anus, 

 which is used as a leaping apparatus. 



CoUemhola are often injurious to seedling plants {Achorutei 



Silver Fish 

 {Lepisma sacchnrina). 



