In this class the antennæ are apparently wanting, wings are never present, and the adults are usually provided with four pairs of legs. Scorpions, harvest-men, spiders, mites, etc.
HEXAPODA (Insects)
True insects have a single pair of antennæ, which is rarely vestigial, and usually one or two pairs of wings in the adult stage. Familiar examples are cockroaches, crickets, grasshoppers, bugs, dragon-flies, butterflies, moths, mosquitoes, flies, beetles, ants, bees and wasps.
ORDERS OF THE ARACHNIDA
a. Abdomen distinctly segmented. A group of orders including scorpions, ([fig. 11]), whip-scorpions ([fig. 10]), pseudo-scorpions, solpugids ([fig. 12]) harvest-men (daddy-long-legs or harvestmen), etc. Arthrogastra
aa. Abdomen unsegmented, though sometimes with numerous annulations Sphærogastra
b. A constriction between cephalothorax and abdomen ([fig. 7]). True Spiders Araneida
bb. No deep constriction between these parts.
c. Legs usually well developed, body more or less depressed ([fig. 49]). Mites Acarina
cc. Legs stumpy or absent, body more or less elongate or vermiform, or if shorter, the species is aquatic or semi-aquatic in habit.