1 62 The Orders of Insects 



cases. Orders, like species and families, are often 

 hard and sometimes impossible to define; our "little 

 systems " can but imperfectly express our imperfect 

 knowledge of the creatures we study. And when 

 it is extremely doubtful that a number of families 

 are really akin to one another, despite their common 

 possession of certain superficial characters, it is better 

 not to include them in a single order and thereby 

 imply their kinship. Accordingly, in the arrange- 

 ment here suggested, the old Neuroptera have been 

 distributed among several orders. 



Order i. Collembola (Springtails). — Wingless insects with not 

 more than six apparent abdominal segments, of which the 

 first usually bears a ventral tube and the fourth or fifth a 

 spring consisting of a pair of partially fused limbs. Jaws 

 withdrawn into the head. No metamorphosis. 



Order 2. Thysanura (Bristletails). — Wingless insects with ten 

 abdominal segments, most of which bear short pairs of limbs, 

 the hindmost pair usually forming long cercopods. No meta- 

 morphosis. 



Order 3. Dermaptera (Earwigs). — Insects witli biting jaws, the 

 second maxilla; incompletely fused ; with small leathery fore- 

 wings, beneath which the delicate hindwings are folded both 

 longitudinally and transversely ; (wings are often absent). 

 A pair of forceps at hinder end of body. Genital ducts 

 without chitinous lining. Kidney-tubes numerous. No 

 metamorphosis. 



Order 4. Orthoptera (Cockroaches, Leaf-insects, Locusts, and 

 Crickets). — Insects ■with biting jaws, the second maxillse in- 

 completely fused. All wings net-veined, the forewings of 

 firmer texture than the hindwings, which are folded fan-wise 

 beneath them. Kidney-tubes numerous. No metamorphosis. 



Order 5. Platyptera (Biting-lice, Book-lice, Termites, Stone- 

 flies). — Insects with biting jaws and four similar membranous 

 wings (wings are often wanting). Kidney-tubes few except 

 in Stone-flies. Metamorphosis none or slight. (The nymphs 

 of Stone-flies are aquatic with tracheal gills). 



Order 6. Thysanoptera (Thrips). — Insects with piercing and 

 sucking jaws ; mandibles bristle-like, maxills with palps. 

 Fore and hindwings similar, narrow and fringed. Kidney- 

 tubes few. Metamorphosis none or slight. 



