CLASSIFICATION AND GENERAL ORGANIZATION 375 



Order 11, Mecoptera. — This is an order comprising but few 

 known species and none with common names. Mouth parts 

 mandibulate. Wings four, membranous, coarsely veined. Devel- 

 opment with metamorphosis. 



Order 12, Tricoptera. — This order includes the caddis-flies 

 and their relatives. Mouth parts of adult rudimentary, mandibu- 

 late in larva. Wings four, membranous, hairy, posterior pair 

 usually the larger. Development with metamorphosis. Species 



550. 



Order 13, Lepidoptera. — The butterflies and moths (Fig. 195). 

 Mouth parts suctorial in adult, but mandibulate in the larvae, or 

 caterpillars, which feed upon vegetation almost without exception. 

 Wings four, similar, membranous, but covered with scales. Devel- 

 opment with highly specialized metamorphosis in the pupal stage. 

 Species 50,000. 



Order 14, Coleoptera. — The beetles (Fig. 197 and Fig. 306, 

 p. 551). Mouth parts mandibulate. Wings four, but anterior 

 pair modified as wing-covers. Development with metamorphosis. 

 Species 15,000. 



Order 15, Diptera. — The true " flies." :Mouth parts suctorial 

 though modified in various ways, as in the house-fly (Fig. 198) 

 and mosquito (Fig. 199). Wings two, representing the anterior 

 pair; posterior pair rudimentary. Development with metamor- 

 phosis. Species 40,000. 



Order IG, Siphonaptera (Aphaniptera). — The fleas and related 

 insects, all of which are parasitic. Mouth parts suctorial in adult, 

 mandibulate in larva. Wings absent or rudimentary. Develop- 

 ment with metamorphosis. Species 150. 



Order 17, Hymenoptera. — The ants, bees, and wasps (Figs. 200 

 to 207). Mouth parts both mandibulate and suctorial in same 

 adult individual. Wings four, similar, membranous, and trans- 

 parent. Development with metamorphosis. Species 30,000. 



In the foregoing brief descriptions it will be noted that the 

 mouth parts, the wings, and the mode of development have been 

 chosen as the most important diagnostic features of the seventeen 

 orders of the Insecta. A general comparison of the various orders 

 indicates that the more generalized types of insects possess man- 

 dibulate mouth parts, and that even those orders in which the 

 mouth parts are modified in other ways possess mandibles in their 

 larval stages. In the simplest orders of Insecta (Thysanura and 



