112 STRUCTURAL AND SYSTEMATIC ZOOLOGY 



3. Hemiptera, or "bugs," are chiefly characterized by 

 a suctorial mouth, which is produced into a long, hard 

 beak, in which mandibles and maxillae are modified into 

 bristles and inclosed by the labium. The four wings are 

 irregularly and sparsely veined, sometimes wanting. The 

 body is flat above, and the legs slender. The larva differs 

 from the imago in wanting wings. In some species the 

 fore wings are opaque at the base and transparent at the 

 apex, whence the name of the order. Some feed on 

 the juices of animals, others on plants. Here belong the 

 wingless bed bug (Cimex) and louse (Pediculus), the 

 squash bug (Anasd), water boatman (Notonectd), seven- 

 teen-year locust (Cicada), cochineal (Coccus), and plant 

 louse (Aphis). More than twenty thousand species are 

 known. 



4. Dipt era, or " flies," are characterized by the rudi- 

 mentary state of the hinder pair of wings. Although 

 having, therefore, but one available pair, they are gifted 

 with the power of very rapid flight. While a bee moves 

 its wings one hundred and ninety times a second, and a 



FIG. 69. Metamorphosis of the Flesh Fly (Sarcophaga carnaria) : a, eggs; b, young 

 maggots just hatched: c, d, full-grown maggots; e, pupa; f, imago. 



butterfly nine times, the house fly makes three hundred 

 and thirty strokes. A few species are wingless. The 

 eyes are large, with numerous facets. In some forms, as 

 the house fly, all the mouth parts, except the labium, are 

 rudimentary ; and the labium has an expanded tip, by 

 means of which the fly licks up its food. In other forms, 

 as the mosquito, the other mouth parts are present as 

 bristles or lancets, fitted for piercing; the thorax is 

 globular, and the legs slender. The larvae are footless 



