526 INVERTEBRATE MORPHOLOGY. 



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

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

 single pair of legs. Scolopendrella. 



III. Class INSECTA. Trunk differentiated into thorax composed of three 

 rings and an abdomen with typically ten segments. 



1. Subclass Apterygota. Thorax without wings; abdominal segments 



sometimes with rudimentary limbs in the adult. 



1. Order Tltysamira. Abdomen with ten segments, terminating in 



three cerci ; abdominal appendages frequently present. Le- 

 pisma, Campodea. 



2. Order Colleinbola. Abdomen with six segments terminating in 



two spriugiug-organs ; abdominal appendages wanting. Podura, 

 Anurida. 



2. Subclass Pterygota. With usually two pairs of wings situated on 



the meso- and metathoracic segments ; abdominal appendages 

 wanting in adults. 



1. Order Dermaptera. Abdomen with forceplike cerci ; anterior 



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

 transversely ; mouth-parts biting ; metamorphosis gradual. 

 Forficula, Labia. 



2. 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. Caloptemis, Gryllus, Gryllotalpa, Periplaneta, Dia- 

 pheromera. 



3. Order Epltemeridce. 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 Odnnata. Abdomen with two platelike cerci ; wings mem- 



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

 parts biting; metamorphosis incomplete, sometimes approaching 

 completeness. Libelltda, jEschna, Ayrion, 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, Trichodectes. 



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. Thrips, Phlwotl trips. 



