104 THE CLASS OF INSECTS. 



Gei'staecker's estimate. He reckons that there are at least 

 25,000 species of Hymenoptera, 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. 



GuoupiNCr OF Insects into Orders and Suborders. Be- 

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

 present the following tabular view of the Classhlcation of In- 

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

 Insects formed orders and not classes was llrst 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-dass I. Segments grouped into thi'ee distinct re- "1 



gions; eyes compound and simple; two piiirs of j IIexapoda 

 wings:* tliree pairs of tlioracic legs; one pair of ^(Six-footed In- 

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

 complete metamorphosis, . . . . .J 



Sub- class ILSc'^mcnta gfouped into two regions, a^ 



false cephalothorax fund an abdomen; noantennne; I A^\c^^^nA 

 eyes simple; wingless; four pairs of thoracic legs ; y (^ryiA^ra) 

 three pairs of jointed abdominal appendages (spin- I ^ ^ ^' 



ne'rets) often present. No metamorphosis, . . J 



S;ib-rlnss TTLBody cylindrical, worm-like. Segments ^ 

 not grouped into regions. Head free; eyes sim- 

 ple ; antennae present ; wingless ; uuraerous ab- 

 dominal legs present; yelk-sac present for a 

 short period after hatching. No metamorphosis. 



Myriopoda 



(Centipedes). 



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



Mctahola. The body usually cylindrical; prothorax ^ 



small; mouth-parts more generally haustellate | Hymenoptera 



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



pupa inactive; larva usually cyliudrical, very | Diptera. 



unlike the adult, J 



^etrrometabola. The body usually flattened; pro- ^ Coleoptera. 



thorax large and squarish; mouth-parts usually j Hemiptera. 



adapted for biting; metamorphosis in a large }« Orthoptera. 



number incomplete; pupa often inactive; larva j Neuroptera. 



flutteued, often resembling the adult, . . J Thysanura. 



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

 one pair. 



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

 the head being much freer from the 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 



