526 INVEBTEBRATE MOBPHOLOGT. 



4. Order Symphyla.— With only one pair of maxillsB and no maxilli- 

 peds ; antennae simple ; most of the trunk-segments with a 

 single pair of legs. Soolopendrella. 

 III. Class INSEOTA.— Trunk diflEerentiated into thorax composed of three 

 rings and an abdomen with typically ten segments. 

 1. Subclass Apterygota.~T]xovst,:L without wings; abdominal segments 

 sometimes with rudimentary limbs in the adult. 



1. Order Thy sanur a. —KhAomen with ten segments, terminating in 

 three cerci ; abdominal appendages frequently present. Le- 

 pisma, Campodea. 



3. Order Collemhola. — Abdomen with six segments terminating in 

 two springing-organs ; abdominal appendages wanting. Podurg., 

 Anurida. 

 3. Subclass Pterygota. — With usually two pairs of wings situated on 

 the meso- and metathoracic segments ; abdominal appendages 

 wanting in adults. 



1. Order Derinaptera. — Abdomen with forceplike cerci ; anterior 

 wings small and chitinous, posterior folded like a fan and also 

 transversely ; mouth-parts biting ; metamorphosis gradual. 

 Forficula, Labia. 



3. Order Orthoptera. — Abdomen usually with cerci ; anterior wings 

 chitinous, covering the posterior, which fold fanlike and some- 

 times also transversely ; mouth-parts biting ; metamorphosis 

 gradual. Caloptenus, Qryllus, Qryllotalpa, P&i-iplaneta, JHa- 

 pheromera. 



3. Order Ephemeridce. — Abdomen with two long cerci ; wings mem- 



branous and richly veined, the anterior larger ; not folded when 

 at rest ; mouth-parts biting, but reduced ; metamorphosis in- 

 complete. Ephemera. 



4. Order Odonata. — Abdomen with two platelike cerci ; wings mem- 



branous and richly veined, not folded when at rest ; mouth- 

 parts biting; metamorphosis incomplete, sometimes approaching 

 completeness. Lihellida, uEsc7ina, Agrion, Diplax. 



5. Order Plecoptera. — Abdomen usually with cerci; wings membra- 



nous, moderately veined with few cross-veins ; the anterior cov- 

 ering the posterior when at rest ; mouth-parts biting ; meta- 

 morphosis incomplete. Perla. 



6. Order Corrodentia. — Abdomen without cerci ; wings sometimes 



wanting (parasites and neuters), membranous, the anterior cov- 

 ering the posterior when at rest ; mouth-parts biting ; meta- 

 morphosis incomplete or wanting. Termes (with polymorphism) , 

 Atropos, Liotheum, Tn'chodectes. 



7. Order Thysanoptera. — Abdomen without cerci ; wings sometimes 



wanting, narrow, poorly veined, fringed with hairs ; the anterior 

 pair covering the posterior when at rest ; mouth-parts piercing 

 and sucking; metamorphosis incomplete. ThHps, Phlaothrips. 



