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, ¢.¢. 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 » pair of legs, the last two often with 
wings. 
3. The abdomen, usually with ten to eleven segments, withnever 
—inorethan.izansformed 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, 
