214 AN INTRODUCTION TO ENTOMOLOGY 



ancient one; it separated from the Palaeodictyoptera before definite 

 cross-veins in the wings had been developed and has not attained 

 them. It is placed in the table next to the Orthoptera because the 

 wings are specialized by the development of supernumerary veins of 

 the accessory type and are developed externally; but the peculiar 

 specialization of the wings is very different from that of the Orthop- 

 tera as is indicated in the table. And in other respects the termites 

 have reached a stage of development far in advance of that shown by 

 any of the Orthoptera. They have attained a social mode of life, 

 with the correlated separation of the species into several castes and 

 the development of remarkable instincts. In this respect they rival 

 the social H^nmenoptera. 



In fact the living members of each of the orders of insects must be 

 regarded as a group of organisms representing the results of speciali- 

 zation in a direction different from that of any other order; and to 

 attempt to decide which order is the "highest" seems as futile as the 

 discussion by children of the question: "Which is better, sugar or 

 salt?" The list below indicates the sequence in which the orders are 

 discussed in the following chapters. 



THE SUBCLASSES AND ORDERS OF THE HEXAPODA 



SUBCLASS APTERYGOTA. — Wingless insects in which the wingless condition is 

 believed to be a primitive one, there being no indication that they descended 

 from winged ancestors. 



ORDER THYSANURA. — The Bristle-tails. p. 220. 



ORDER COLLEMBOLA. — The Spring-tails. p. 225. 



SUBCLASS PTERYGOTA. — Winged insects and wingless insects in which the 

 wingless condition is believed to be an acquired one; i. e., those insects that 

 have descended from winged ancestors. 



ORDER ORTHOPTERA. — The Cockroaches, Crickets, Grasshoppers, and others, 

 p. 230. 



ORDER zoRAPTERA. — The genus Zorotypus. p. 270. 



ORDER isoPTERA. — The Termites or White Ants. p. 273. 



ORDER NEUROPTERA. — The Dobson, Aphis-lions, Ant-lions, and others, p. 281. 



ORDER EPHEMERiDA. — The May-flics. p. 308. 



ORDER ODONATA. — The Dragon-flies and the Damsel-flies, p. 314. 



ORDER PLECOPTERA. — The Stone-flies. p. 325. 



ORDER CORRODENTIA. — The Psocids. p. 33I. 



ORDER MALLOPHAGA. The Bird-lice. p. 335. 

 ORDER EMBHDINA. — The Embiids. p. 338. 

 ORDER THYSANOPTERA. — The Thrips. p. 341. 



ORDER ANOPLURA. — The LicC. p. 347. 



ORDER HOMOPTERA. — The Cicadas, Leaf-hoppers, Aphids, Scale-bugs, and 

 others, p. 394. 



ORDER HEMiPTERA. — The True Bugs. p. 350. 



ORDER DERMAPTERA. — The Earwigs. p. 460. 



ORDER COLEOPTERA. — The Beetles, p. 464. 



ORDER STREPSIPTERA. — The Twisted Winged Insects, p. 546, 



ORDER MECOPTERA. — The Scorpion-flies. p. 550. 



ORDER TRICHOPTERA. — The Caddice-flies. p. 555. 



ORDER LEPiDOTERA. — The Moths, the Skippers, and the Butterflies, p. 571. 



ORDER DiPTERA. — The Flies. p. 773. 



ORDER siPHONAPTERA. — The Fleas, p. 877. 



ORDER HYMENOPTERA. — The Bees, Wasf)s, Ants, and others, p. 884. 



