104 THE CLASS OF INSECTS. 



Gerstaecker's estimate. He reckons that there are at least 

 2o,000 species of Ilymenoptera, from 22,000 to 24,000 Lepidop- 

 tera, about 24,000 Diptera, and 90,000 Coleoptera ; the number 

 of the other suborders cannot be easily estimated. Besides 

 these there are about 4,600 Arachnida, and 800 Myriopods. 



Grouping of Insects into Orders and Suborders. Be- 

 fore beginning an account of the Six-footed Insects, we 

 present tlie following tabular view of the Classification of In- 

 sects. Tlie idea that the Myriopods, Spiders, and Six-footed 

 Insects formed orders and not classes was first proposed by R. 

 Leuckart in 1848, and afterwards supported by Agassiz and 

 Dana. The arrangements proposed by these and other authors 

 are put in tabular form on page 106. 



The Class of Insects. 



Sub-class I. Segments grouped into three distinct re- ^ 



gioiis ; eyes compound and simple ; two pairs of j Hexapoda 

 wings:* three pairs of thoracic legs; one pair of )« (Six-footed In- 

 jointed abdominal appendages. A more or less | sects). 

 complete metamorphosis, . . . . .J 



Sub-class II.Seix,mGiit^ grouped into two regions, a") 



false cephalothorax land an abdomen; noantennje; j Ar-vchxida. 

 eyes simple ; wingless ; four pairs of thoracic legs ; )■ csoiri .,• • V 

 three pairs of jointed abdominal appendages (spin- I ^ ^ e *>;. 

 nerets) often present. No metamorphosis, . . J 



Sxh-dass TTLBocly cylindrical, worm-like. Segments "j 



not grouped into regions. Head free ; eyes sim- j Myiuopoda 

 pie; antennae present; wingless; numerous ab- '> cceutipedes") 

 dominal legs present; yelk-sac present for a | *^ ^ ■'' 



short period after hatching. No metamorphosis. J 



The Orders of Six-footed Insects f (Hexapoda). 



Metahola. The body usually cylindrical; prothorax 'j 



small; mouth-parts moi-e generally haustellate | Hymexoptera 



(formed for sucking) ; metamorphosis complete ; )■ Lkpidopteka. 



pupa inactive ; larva usually cylindrical, very | Dipteua. 



unlike the adult, J 



leterometabola. The body usually flattened ; pro- S Coleoptera. 



thorax large and squarish ; month-parts usually | Hemiptera. 



adapted for biting ; metamorphosis in a large )■ Orthoptera. 



number incomplete; pupa often inactive; larva Neuroptera. 



flattened, often resembling the adult, . . J Thysanuka. 



* The number of wingless forms is comparatively few. The Diptera have but 

 one pair. 



tTlic so-called "cephalothorax" of Spiders is not like that region in the Crabs, 

 the head being much Ireer from tlie thorax. 



X Leuckart's classification is an advance on others in his considering the Hexa- 

 poda, Arachnida, and Myriapoda as orders instead of classes, but he says nothing 



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