12 INTRODUCTION. 



water have hind legs more or less flattened and fringed 

 with long hairs, which tiiey use as a boatman does his 

 oar; forms of these oar-like feet may be seen in Dyticus, 

 Notonecta, and Gyrinus. The mole cricket, like its 

 mammalian namesake, has its fore legs very short and 

 strong, the tibia being cut into finger-like projections 

 suited to its burro v/ing habits; in the water scorpion 

 (Nepa cinerea) the fore legs are converted into a pair 

 of nippers, by means of which the insect seizes and 

 retains hold of its prey. 



The wings of an insect are beautiful and interesting 

 objects ; they are attached to the second and third 

 segment of the thorax ; each wing consists of two 

 membranes with a number of veins or nervures between 

 them, which ramify in various directions and help to 

 keep the wings extended. Some insects have only two 

 wings, others (the greater number) have four, which are 

 either of a similar texture throughout, and are all 

 available in flight, or else the anterior pair have a con- 

 sistency like horn, and form a sheath or covering 

 for the hinder wings when the insect is at rest; when 

 in flight these wing-cases are kept still, being at right 

 angles with the body. These are known by the name 

 of Elytra, from the Greek eXvTpov " a cover" or " case," 

 used for the shard of a beetle's wing as early as the 

 time of Aristotle. All beetles (Coleoptera) — not the 

 so-called " black beetles" of our kitchens, which are 

 not beetles at all — possess these horny pair of wing 

 covers, hence the term which has been given to the 

 order, from koXioq " a sheath," and irrspov ** a wing." 

 In some insects the basal part of the elytra is horny, 

 the top part being membranous. Tlie Diptera or 



