500 ARTHROPODA. 



of long legs on each; close behind the head are a pair of j^oison 

 feet. 



43. The Hexapoda have the body divided into head, thorax, 

 and abdomen. 



43. The abdomen consists of a varying number of somites and 

 lacks appendages. 



44. The thorax consists of three segments, pro-, meso-, and 

 metathorax, each bearing a pair of legs, and meso- and metathorax 

 usually a pair of wings each. 



45. The head bears, besides three jiairs of month parts, an un- 

 paired upper lip (labrum) and two compound e3'es, besides usually 

 one to three ocelli. 



46. The structure of the mouth parts varies with the food; 

 they are cither biting, licking and sucking, or piercing in function. 



47. Wingless insects iisnally have a direct (ametabolous) de- 

 velopment with numerous ecdyses. 



48. Winged insects (and many vyithout wings which have de- 

 scended from winged forms) have a metamorphosis in which the 

 larva differs more or less from the imago (metabolous insects) : the 

 larva never has wings. 



40. An incomplete metamorphosis (heniimetaljoloiis develop- 

 ment) occurs when the larva with each molt becomes more like 

 the adult, developing wing pads which with each ecdysis become 

 larger. 



50. In complete metamorphosis (holometabolous development) 

 the changes occiir in the last molting stage, which is a stage of 

 rest, the pupa. 



51. Classification of Hexapoda is based ujion structure of mouth 

 parts and wings as well as upon regional relations and development. 



53. The Apterygota are wingless, ametabolons Hexapoda with 

 biting mouth parts. 



5.3. The Archiptera have biting mouth parts with incompletely 

 fused labium, net-veined wings, and incomplete metamorphosis. 



54. The Ortlioptera resemble the Archiptera in mouth jiarts 

 and development, but have 2«irchment-like wings. 



55. The Neuroptera have net-veined wings and a holometabolous 

 development; the mouth parts are modified. 



56. The Coleopte.ra are biting insects with the fore wings 

 changed to elytra; they differ from the somewhat similar Orthop- 

 tera by the complete metamorphosis. 



57. The Strepsiptera are parasitic foruis allied to the Coleopterix. 



58. The IIijmenopte7-a have partly biting, partly licking mouth 



