212 AN ITRODUCTION TO ENTOMOLOGY 



plete metamorphosis, which also doubtless arose independently in 

 different divisions of the insect series, as, for example, intheNeurop- 

 tera, which it is believed is a very ancient order, the origin of which 

 was much earlier than the attainment of complete metamorphosis. 



TABLE OF THE METHODS OF SPECIALIZATION OF THE WINGS CHARACTERISTIC 

 OF THE ORDERS OF WINGED INSECTS* 



This table is merely the result of an effort to indicate the more striking of 

 the methods of specialization of the wings characteristic of each of the orders 

 of insects. It is not a key for determining the orders of insects. It is not avail- 

 able for this purpose; because, in many cases, the wings of an insect do not 

 show the type of specialization characteristic of the order to which the insect 

 belongs. Thus, for example, while the most characteristic modification of the 

 courses of the wing-veins in the Diptera and Hymenoptera is due to the coales- 

 cence of veins proceeding from the margin of the wing towards the base of the 

 wing, there is no indication of this type of coalescence of veins in some of the 

 nemocerous Diptera. 



A. Wings specialized by the development of supernumerary veins in the preanal 

 area. 

 B. Supernumerary veins of the accessory type. 

 C. Wings developed externally. 



D. Wings retained throughout life. Wings without a striking contrast 

 in the thickness of the veins of the anterior part of the wing and those 



of the middle portion Orthoptera 



DD. Wings deciduous, there being near the base of each wing a trans- 

 verse suture along which the wing is broken off after the swarming 

 flight. Wings with the veins of the anterior part of the wing greatly 

 thickened and those of the middle portion reduced to narrow lines 



ISOPTERA 



CC. Wings developed internally Neuroptera 



BB. Supernumerary veins of the intercalary type. 



C. Flight -function cephalized; the hind wings being greatly reduced 



in size Ephemerida 



CC. Flight-function not cephalized; the hind wings as large as or larger 



than the fore wings Odonata 



AA, Wings specialized by a reduction in the number of veins in the preanal 

 area. 

 B. Wings developed externally. 



C. The two pairs of wings similar in texture. 



D. With the tendency to develop accessory veins retained. . Plecoptera 

 DD. With the tendency to develop accessory veins in the preanal area 

 lost. 

 E. With the courses of some of the longitudinal veins modified so 



that they function as cross-veins 'oRRonFNTTA 



EE. The transverse bracing of the wing attained in the usual way. 

 F. The veins of the wing bordered with dark bands.. .Embiidina 

 FF. The veins of the wing not bordered with dark bands. 



G. Wings long and narrow, supplemented by a wide fringe of 



hairs Thysanoptera 



GG. Wings not greatly narrowed and not supplemented by a 



wide fringe of hairs Homoptera 



CC. The front wings more or less thickened. 



D. The front wings not greatly reduced in length as compared with 

 the hind wings. 



E. The front wings thickened throughout Homoptera 



EE. The front wings thickened at the base, the terminal portion 



membranous Heteroptera 



DD. The front wings greatly reduced in length Dermaptera 



*From "The Wings of Insects," pp. 120-122. 



