104 . THE CLASS OF INSECTS. 



Gerstaecker'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 Myriapocls. 



GROUPING OF INSECTS INTO ORDERS AND SUBORDERS. Be- 

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

 present the .following tabular view of the Classification of In- 

 sects. The idea that the Myriapods, 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. 



Order I. Segments grouped into three distinct re- 

 gions ; eyes compound and simple ; two pairs of 

 wings:* three pairs of thoracic legs; one pair of 

 jointed abdominal appendages. A more or less 

 complete metamorphosis, 



Order //.Segments grouped into two regions, a 

 false cephalothorax f and an abdomen ; no antennas ; 

 eyes simple ; wingless ; four pairs of thoracic legs ; 

 three pairs of jointed'abdominal appendages (spin- 

 nerets) often present. No metamorphosis, . 



Order III. Body C3 r lindrical, worm-like. Segments 

 not grouped into regions (except in the recently 

 hatched young). Head free; eyes simple; an- 

 tenna? present; wingless; yelk-sac present for a 

 short period after hatching. No metamorphosis, 



HEXAPODA 

 (Six-footed In- 

 sects). 



ARACHNIDA 



(Spiders). 



MYRIAPODA 



(Centipedes). 



THE ORDER OF SIX-FOOTED INSECTS J (Hexapoda}. 



First and higher series. Body usually cylindrical ; ) 



prothorax small; mouth-parts more* generally | HYMENOPTERA. 

 haustellate (formed for sucking) ; metamorphosis }>LEPIDOPTERA. 

 complete ; pupa inactive ; larva usually cylindri- | DIPTEHA 

 cal, very unlike the adult, . . . . . } 



Second and lower series. Body usually flattened ; "| r 



prothorax large and squarish ; mouth-parts usually | V T ,. PT ' 

 adapted for biting; metamorphosis incomplete; ^Arjr 

 pupa often inactive ; larva flattened, often resem- i ^ 

 bling the adult, . . . . . . . J NEUROPTERA. 



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

 one pair. 4 



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

 the head being much freer from the thorax. 



JLeuckart'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 



