GENERAL NOTES ON INSECTS. 339 



CLASSIFICATION OF INSECTS 



I. Primitive wingless insects, Apterygota or Aptera, including 

 Thysanura, e.g. Machilis, Campodea, Lepisma ; Collembola, 

 Springtails, e.g. Podura, Smynthurus. 



II. Winged insects, Pterygota (in some degenerate forms the wings 

 have been lost). 



A. With mouth -parts usually adapted throughout life for biting 



(Menognathous), with no metamorphosis (Ametabolic) or 

 with incomplete metamorphosis (Hemimetabolic). 



e.g. Orthoptera (cockroach, locust, cricket, etc.); 

 Corrodentia (Termites, bird - lice) ; Odonata 

 (Dragon-flies) ; Ephemerida (May-flies) ; and 

 Dermaptera (Earwigs). 



B. With mouth -parts adapted in the main as suctorial 



organs (Menorhynchous), usually with no metamorphosis 



(Ametabolic). 



e.g. Rhynchota or Hemiptera, e.g. Phylloxera, aphides, 

 coccus insects; Cicadas; bugs; water-scor- 

 pions, lice. 



C. With complete metamorphosis (Holometabolic), with 



mouth-parts always adapted for biting (Menognathous), 

 or adapted at first for biting and afterwards for sucking 

 (Metagnathous). 



e.g. Coleoptera (beetles) ; Diptera (two-winged flies) ; 



Lepidoptera (butterflies and moths) ; Hymen- 



optera (ants, bees, and wasps). 



GENERAL NOTES ON INSECTS 



The main characteristics of insects have already been 

 described in the two types chosen, but we here revise them 

 in general terms. 



Form. The body of an adult insect may be divided into 

 three distinct regions : 



1 . The head, probably consisting of seven fused segments. 



2. The median thorax, divided into pro-, meso-, and meta- thoracic 



segments, each with a pair of legs, the last two often with 

 wings. 



3. The abdomen, usually with ten to eleven segments, with never 



more than transformed traces of appendages. 



Within these limits there is great variety of form, e.g. the long 

 dragon-fly with its large outspread wings, the compact cockchafer, the 

 thin-waisted wasps and long-bodied butterflies, the house-fly and 

 cricket, the large moths and beetles, and the almost invisible insect 

 parasites. 



